City of Heroes and they stop mid-fight to tinker with their Enhancements, which is even worse.)
The problem is that these sorts of behaviors aren't bad things by themselves -- none of them have a major impact on gameplay, and they're not large enough to force an argument or discussion. But they irritate you, even though they're not a big deal, and you can't help but notice them. What sort of stupid human tricks bother you when you're playing? People looting in combat? Not mentioning when they need a quick break to recharge? Talking too much or too little? Let us know!