I know this is a really minor peeve of mine, but it can drive me to distraction on the train.
Sniffing.
If I find myself with any runniness in my nose in the morning, I take tissues with me so I can blow my nose, but there are plenty who don’t. Come the cold season(s), people sniff on the train. I suppose now’s a hayfever season which may be why a chap near me RIGHT NOW is sniffing.
AAARRRGGHHHHH!