I have me own collection of bad habits as well, aye.
From time to time, there have been times Vespian has chewed on the nails, although more severe than that is I tend to chew on the very flesh of my hands and the inside of my cheeks. T'is due to anxiety and it occurs impulsively and subconsciously. What's bad about it is once I begin to chew, it's difficult to stop. Countless times I've made my hands and inside of my mouth bleed as a result. Although over recent months, the habit has gotten better.
I share the similiarity of laughin' when I should not. It occurs mainly when Vespian is nervous or under pressure. A majority of this has already been explained by madam Jackdaw.
Lastly, whenever I'm endulged in somethin' (mainly be it research or just fiddlin' over my own thoughts), I tend to murmur whatever's on my mind underneath my breath. This doesn't happen a lot but when it does, kinda makes I seem a bit out of sorts speakin' rapidly in low whispers. Me guesses that's deemed a bad habit.
Also, sayin' this mere in case, I'd appreciate it if those sharin' their habits keep it appropriate, knowin' good and well some habits are best left unmentioned here.