I was talking about guild wars with a friend and I had an idea:
the game mode is deathmatch, If I meet a friend, I aim him and I push group ctrl forward or group ctrl back (like for recruiting). My friend get a message, if he push conversation yes, my friend's dot on the radar get an another color ant that unlock a frienly fire between us (I create a team). If he dead, he still on my team. For leave the team, he just have tu push group ctrl forward or group ctrl back a few seconds...
I guess it's unrealizable but I just wanted to show my idea