My favourite fellow unnerving travellers have been the religious ones. One time a guy stood at the back of an empty Y cabin in the middle doing the cross thing for about 15 mins before take off.

Then there was the group of about 20 orthodox Jews who JFK-LON started tucking into massive Tupperware containers of hot soup. Best not to wonder where they got the liquid from. We come to takeoff the guys are praying rocking back and forth and the kids are running up the aisle DURING takeoff. The adults don't even realise as they're mid flow.

Then the most common fellow traveller I always come across when flying to the US. The 'ESTA?' crowd. Seemingly there's a rock somewhere that a lot of people are living under completely unaware ESTAs are required for travel to the US.