This is a bit of a tricky one. If it was about which class / race combo I'd *like* to be IRL, I'd have no trouble; that would be troll shaman. I'd love to be as cool & dangerous as a troll, and ankh and astral recall sure would prove handy. Even I could manage to avoid dying IRL more than once an hour, so I'd effectively be death-proof.
In my more crotchety moments, I'd like to be a forsaken afflock, bringing slow, agonising death to those who cross me. Boring presentation? Haha! Curse of tongues! Spy a smug-looking jogger out of my window on a winter morning? Haha! Curse of exhaustion! Annoying people getting in my way in a supermarket? Fear should do the trick!
Unfortunately, the question is about what I'm really most like. The sad truth is that I'm closer to being a follower of The Way of Rincewind than the Way of the Warrior, so melee classes are right out. I tend to solve problems with my head, so mage seems the closest fit. As for race, I'd say gnome, but that would leave me a little ... short. So I'll go for three drunken gnomes standing on each other's shoulders to try to get into a bar. That's about right height-wise, plus it has the requisite level of coordination and balance.