Never heard of any 'nail biting deaths'; yes, it's gross, but there're reasons' people do it & just can't help it! It's a singular affect situation: you & you, alone. Doesn't impinge on anybody else, unless it's their eyes' seeing the nails!
Smoking! Gross, filthy, smelly, stinky, harmful to all & clothes & downright dangerous! It KILLS!
Surely published research has been around long enough by now to discourage this foul habit! But obviously not, & people are starting smoking at even a YOUNGER age!
Hate it when you get into a lift & a smoker has got out before you! It stinks! Where're the extractor fans?
When a work colleague returns from 'smoko' & the smell wafts in the office & they smell to the point of sickly. Don't they know this, or do they have a 'couldn't care less about anybody else' attitude? Foul, just foul!
I dislike both equally. I couldn't live with either. Although having said that, I would be less worried about smoking as that is just an addiction but nail-biting is usually a symptom of something deeper so would worry me more. But I would be extremely unlikely to ever get close enough to a nail-biter or a smoker to be giving it too much thought anyway....
As I bite MY nails, (sorry everyone,) I also have to say defiantly smoking! It's awful walking along footpaths, while people are standing there, puffing away. And when they're smoking in NON smoking zones, e.g., Martin Place Sydney! They should be fined!