Whenever I pull off Ganoncide on someone, I just kinda laugh like "hoyheehoyheehoyheehoy," to be as obnoxious as possible.

Granted, I don't play Ganon all that often.

When I get a Ganoncide I either say "TO THE ABYSS WITH YOU!" or "THERE IS NO SLAMMING THE GANON!" Depending on the situation (The latter being for attempted Meteor smashes.)