Lovely, this thread.
After reading arguments on both sides, I'm going to settle with a public warning.
Ќɨjąj๏µţ€h, just because someone doesn't play to your style, doesn't mean you can report them. Except in cases of obvious trolling (Heavy using shotgun only, pyro using melee only, sniper using smg only, etc...), you cannot report them. The !rep system is primarily in place for those players who go AFK, or for obvious trolling.
A pyro killing people instead of spy checking does not fall under that category. And if he's top fragging? Great! It means your pyro knows what hes doing.
WARNED
Why do mathematicians confuse Halloween and Christmas? Because 31 Oct = 25 Dec!