I'm incapable of taking anything seriously. I'll generally manage it if it really does matter, but I always end up getting caught in double-entendres or ways in which something someone else said in front of me was actually pretty clever. Especially if said person didn't notice just how clever they sounded.
That and I've got this chipped-out segment of my left front incisor that I keep sticking a finger to when I'm idling or just watching TV. I'll press hard, having this weird and fairly childlike "game" of trying to turn that indentation in my tooth into a raised-up bit of my thumb's skin. Thankfully, it makes me look more like a nail-biter than a thumb-sucker.
If I do manage to see a tiny little bump in the middle of the bigger divot caused by my tooth's pressure against my finger, I have this little surge of exultation. Like, "Yay, I'm getting another look at a slight case of dental abuse one of my dentist's hygienists caused me in trying to get to a tiny bit of food that got encased in growing enamel!"
Suffice it to say, it looks real freaking dumb when I do that in public. I mostly manage to repress that urge for office hours. Once I come home, though, I'm like a Parkinson's sufferer who just *has* to let go and let all that pent-up dyskinesia happen. My hand goes to my mouth and unless I'm talking to someone, eating, typing something or stuck in a social event, I'm pretty much always messing with that indent. It's a solidly implanted tic, to put it mildly.
I'm also a real-life Grammar Nazi. Common mistakes don't trigger me, but big and egregious mistakes in French make me blurt out a correction without even stopping to consider if I've hurt someone's feelings in the process. I know it sometimes makes me come across as being pedantic, but I just can't help myself.
I also talk to myself a lot, mostly to try and road-test characters or concepts. It got to the point where the folks tried to stage an intervention, thinking I was in need of some, well, assistance.