ok so this glitch can be a pain sometime but you can do it any level any match
so basically what your going to do is choose the side, costume, wep you want for the match when you go in obviously
1: ur gunna switch to nades and start cooking it
2: so the second you start cooking you are gunna go to the pause menu and get ready to switch teams (doesnt matter what gun what costume etc...)
3: the second the nade explodes you switch teams!
4: while your waiting to respawn your going to go to the pause menu and get ready to switch back to your previous class (same costume and wep as you first chose going into the game)
5: the hard part is right here it takes some getting use to, but basically the second your character hits the ground your going to switch back
6: your going to leave the game once you see the respawn clock again.
7: go back into the game you were in and choose your very FIRST class
if done correctly you should be gm, and now you can piss people off!!!!
ALTERNATE WAY:
so basically the alternate way is instead of cooking the nade you create a game, you need to have good reflexes but basically you get your player options menu ready like in step 2. the second the game starts you switch teams and do step5-7.
this is often harder for me so i just do the nade way, yes it will give you two deaths with the nade way bit if your gm it doesnt matter you can get them back =)