Due to the difficulty in homeless having sexual intercourse, ratting is the process where Street Rats are captured, decapitated and then thrust upon by Male homeless people. The resulting carcass is considered as being 'Ratted'.
"Here Jethro, I just got a big brown one, you want to two's up on a ratting session?"
This refers to when a person in a video game applies techniques of keeping them hidden and using their abilities to catch a person by surprise. It is mostly associated with those who extract camp and camp in corners to surprise players and kill players.
Timmy: Man, I just died to a dude ratting in the corner
Chad: Let me use a grenade to force him out
The Rat dies due to a lack of skill