ZeroMachine said:
Definitely smoking.
Smoking, and, although this may be a given, lying.
Had to deal with both at the end of the last one...
I think the key factor would be 'excessive or addictive'. So smoking, hard drugs, alcoholism (because very few of us would be against a partner getting a little trashed every now and then, but most of us would be against him/her being a chronic drinker).
So yeah, for me the biggest turn offs are addictions and that thig where people go that bit too far (with anything really, whether it be the gym, pets, talking about games, whatever, there is just that point where it goes from 'interest/hobby/whatever to 'obsession/compulsion'). So really, the things that turn me off are things that are 'too far', it's hard to explain, but if you've seen it happen then you'll know exactly what I'm talking about.