This achievement can be unlocked by playing any of 9 classes, on any map and gamemode.
Basically, this achievement can be obtained by playing a lot Team Fortress 2.
If you want to deal with it achievement faster, I have an idea for you.
1. Join with your friend empty on empty server.
2. You friend need to be the spy.
3. Let him backstab you 4 times, then he will get domination.
4. Kill him in response, getting a revenge in result.
5. Repeat 4 more times.
An achievement will be completed after getting a final 5th revenge.