I heard someone say "There's no way you are not hacking, u can kill me in 3 shots with UMP"...
My fav's are people putting in "noob" after weapon I use to get kills.. as in, if I use a shotgun its "shotty noob", if I use UMP, its "ump noob" and if I use nades to kill... i get called "nade noob". If I use G36e, its "g36 noob"... and the rest of the guns are "hacker noob".
I usually deal by saying "I am not hacking, but I know you are. I have proof".. then ignore their desperately emotional retaliation while I get kills.