First, let's do Kenny:
Have him walk in the lake with a metal bar during a thunderstorm
Send him camping at Camp Crystal Lake
Have his hand cut off and make him die of hemmorage
Have him go to a Hanson concert
Just make him commit suicide!
Now other characters:
Mr. Mackey: We saw in Ike's Bris that his tie makes his head big so why not tighten it more and have his head explode!
Ike: Have Kyle play "Kick the Baby" with him in the ceiling fan part at Menards
Stan: Have Scuzzlebutt come back from the dead and have revenge on him
Ned: Have him try another try with a grenade but this time have it blow his head off!
Barbrady: Give him a note that says "Hey dummy! There's a killer behind you!" since he can't read