BO, cursing, toplessness: What you can’t do on a plane

The news that two teenager girls were refused travel on a United Airlines last weekend for the offence of wearing leggings set off a wave of outrage on social media. As with many such outbreaks of mass indignation, the story turned out to be a little more complex than first reported. The women were travelling on so-called "buddy passes", a discounted family rate that comes with more strings attached than a regular ticket, and they were permitted to fly – after they put on other clothes.

Even so, it did raise questions about the rules airlines can impose on travellers. Are there really restrictions about what passengers can wear? Who decides if the slogan on a T-shirt is funny or merely offensive, as in the case of a man barred from a Delta flight in New York because of a slogan than read “Terrists gonna kill us all”?

In reality, few airlines have an explicit dress code. But each has a “code of carriage”, which makes it clear what you can and can’t get away with when flying. Here are 15 of the lesser-known rules (and a couple of under-utilised perks):

1. If you want to fly Virgin, you must be wearing "top and bottom apparel". Virgin's dress code is two lines long: "Any guest who is not wearing both top and bottom apparel" can be refused travel." Further, clothing that is offensive or might interfere with the safety of the flight or safety of other guests is prohibited."

2. If you're flying on a domestic flight in the US, allow time for a shower. If you're a bit whiffy, United, Virgin, American Airlines and Delta can all refuse you travel over your "malodorous condition".

3. Reasons you might be refused travel on Ryanair include being drunk, not having paid for a previous flight, or having once tried to light up on board.

Ryanair’s comprehensive list of reasons a passenger can be refused carriage is similar to other airlines, among them misconduct, including being drunk or impaired by drugs; refusing to pay for your ticket; not having valid travel documents; and refusing to submit to a security check. It also states that “you owe us any money in respect of a previous flight” or “you cannot prove that you are the person named in the Boarding Pass”.

4. You can be refused travel on an Aer Lingus if you have a contagious illness or act in an insulting manner towards ground crew. Aer Lingus's rules for refusing travel are similar to rival Ryanair's, except that it also explicitly states that you can be turned away for having a "contagious infectious condition" or behaving in an "insulting" manner towards ground crew.

5. If you are travelling Ryanair, don't bring energy-saving lightbulbs, contact lenses, sunglasses or your camera in your suitcase. And leave the lawnmower and hunting trophies at home.

Ryanair has a long list of items it won’t allow in the hold. Some of these (Christmas crackers, lawnmowers, Samsung Galaxy Note 7s) don’t require much explanation. More surprising prohibited items include “money, jewellery, precious metals, keys, cameras, computers, medicines, spectacles, sunglasses, contact lenses, watches, mobile phones, tablets, personal electronic devices, negotiable papers, securities, cigarettes, tobacco or tobacco products or other valuables, business documents, passports and other identification documents or samples.”

Ryanair's reason for banning these is simple: if they go missing, the airline is not liable as it told you not to bring them. Aer Lingus is less restrictive, banning only "money, jewellery, precious metals, computers, personal electronic devices, negotiable papers, securities or other valuables, business documents, personal medication, passports and other identification documents or samples".

6. Attention Delta passengers: if you must travel with a Christmas tree, make sure you wrap it up. Delta might have strong views on slogan T-shirts, but is unfazed by passengers toting unconventional items on board. "Who are we to turn away holiday spirit?" the airline states. "We allow cut Christmas trees as limited release baggage on all flights . . . subject to baggage allowance and size guidelines."

7. Don't fly barefoot. Most airlines don't have an explicit published dress code, but almost all have a rule that passengers must be wearing shoes.

8. Watch your language on Etihad Airways, which retains the right to refuse travel if you use "indecent words" to ground staff or members of the crew.

9. Ferrets, dogs and cats can legally travel to Ireland from other parts of Europe, provided they have a passport. You can also bring a pet bird, rabbit or rodent from another EU state, so long as you accompany the pet to Ireland. But all that depends on finding an airline willing to take them.

Aer Lingus will transport your dog or cat in the hold on regional flights, or you can book them as cargo within Europe for €160 per crate (freight forwarding fees may also apply). It won't take puppies under 10 weeks old, mink, wild birds, dangerous dog breeds, Persian cats or pugs. Ryanair won't transport any pets on board, and only allows assistance animals on certain routes.

10. It can be cheaper to book a suitcase in your child's name instead of your own. A little-known Ryanair perk allows families to save 50 percent off the cost of a 15kg bag by booking it in their child's name.

11. Ryanair will give frequent flying families 20 per cent off their third set of return flights in the same year. You must meet the following conditions: there's one adult and one child under 15 in your group; you're flying with the same group; and you paid for one "extra" on your two previous flights. Before you make the third booking, fill out a form on the Ryanair website and get a code to use within four weeks.

12. If your flight is cancelled, you are entitled to meals, refreshments and the cost of two telephone calls, texts or emails. You can also claim overnight accommodation if you are pushed to the next day.

13. Delayed for more than three hours? Thanks to rule EU 261, you may be entitled to cash. For delays over three hours, except those caused by "extraordinary circumstances which could not have been avoided by reasonable measures", you are entitled to compensation of €250 per person on short-haul flights. For medium haul it's €400 and for long haul it's €600.

14. Need a plaster or a tampon? Want seconds? Forgot your pyjamas? Ask, but be nice. But pack your own painkillers as cabin crew are not permitted to dispense medication. But if you want a second portion of dinner, or you quite fancy a pair of airline pyjamas (usually only available in first or business class), frequent flyers advise that it is always worth asking. But be polite: cabin crew can make magic happen if they like you.

15. If you miss your flight in the US, ask about the "flat tyre" rule. Some airlines in the US – including Delta, Southwest and United -- have this unwritten policy, meaning they will let passengers held up through no fault of their own fly standby on the next flight without having to pay to rebook. (Anecdotally, they are becoming more stingy about offering it.) European airlines do not have an equivalent.