My main game for these moments is Aliens vs. Predator 2 (also, any fans? Could have a game sometime) as it's the one game I'm genuinely godlike at. My best moment I would say was on an evacuation (marines get to a point and hold against aliens) where I rushed forward as a single alien drone - I destroyed the whole squad of marines by myself, the team including:
1 Exosuit
2 Pulse-Rifle armed Marines
1 Flamer
1 Heavy Weapons (Sadar)
5 Kills was the queen kill limit, so the next round I was a queen alien, one of two that server had ever seen due to the fact you'd have to take out their whole team by yourself as a regular alien class
Very proud moment, hehe.