Sometimes I have trouble recognizing team mates at TTAC in a particular scrim because the teams get remixed so often. It's not a great excuse to shoot a friendly, but sometimes I get a little jumpy in a fierce CQC engagement with a lot of movement and Jer is just plain dangerous. If I go through the roster every time before shooting him I'd never get a hit on him because he's too quick. My default action is to shoot Jer without prejudice just in case he's not on my team
I try not to get too bent out of shape when I get friendlied at TTAC because I realize that shooters are often either shooting impulsively or shooting at targets who are oriented a particular way. I often have to make a quick decision on who to shoot based on their gun orientation relative to their movement direction.
It's unfortunate, but in rapidly developing situations there are tradeoffs to be made when adhering to deliberate procedures and pouncing on opportunities as they present. I occasionally get team killed when I lunge out to grab an important firing position. I occasionally can shape a game by seizing a good strategic position so I accept that I may provide greater value to my team, but expecting everyone else on my team to be extra careful not to shoot me would degrade their effectiveness far more than my individual value so that's a personal tradeoff I accept. That being said, there is little value to bitching someone out for a teamkill unless they frequently inflict kills on their own team. In that case you should put them where they're less hazardous to everyone. Usually I find that the embarrassment of fratricide is "punishment" enough.