I’ve heard stories about people flying in bathrobes and slippers, maybe that’s what inspired Arthur Dent. I’ve also heard stories about people being kicked off flights for wearing T-Shirts with swear words. It’s probably a different game in middle eastern; all the worse as the airlines may not tell you what their society presumes is normal. If you are flying, dress up for the occasion, but be comfortable.
Usually these just get confiscated, but it is better not to have wasted the money and effort. Counterfeit items, such as imitation watches and fake designed clothing, are banned in many places. A single item can just as easily go unnoticed; the real problem is people buying these in bulk and trying to sell them back home. Best to avoid this situation.
Food items are a different matter- just about any item might prove illegal; and if you don’t declare it then matters are worse. There have been problems with kinder surprise chocolate eggs as the small toys are considered a safety hazard for children.
Avoid animal products. Things like Ivory are illegal because of the threat that the trade imposes on endangered elephants. These laws are there for a good reason.
Some ceramic items like bowls are known to contain large amounts of lead. This is a health threat, so don’t take the risk.
The Wrong Terminal or Airport:
It’s too easy for a search engine to pull up something that looks like the right answer. London has two airports, you have to go to the correct one. Dallas DFW has four terminals marked as the ‘American terminal’; again, you need to know the right one. Plenty of cities have airports that aren’t for commercial lines. It’s too easy to go to an airport rather than the particular airport where your flight departs.
Airport transfer shuttles will get you to the right place in plenty of time. Avoid problems, traffic and hassles by pre-booking an airport shuttle for both the departing and return journey.