Through human psyche...
Chances are he was enraged of the BS smash attacks G&W has, and in some cases you/ whoever taunts, just provokes the typical "THAT'S ALL YOU FREAKING DO!!" response, insult your mother and then leave.
In terms of skill and "Brawl", Stupid attacks that KO at ridiculous %'s that are somewhat not difficult to pull off + Taunting *Insert "PWNED" or "You freaking Suck" taunt* = many reasons to be enraged and enough motive to call ANYONE a spammer.
But this is all theory :P