This glitch happened to me twice by accident:
Okay, sometimes if you see a Kecleon Shop in a dungeon, there might be several traps around the carpet that holds his inventory, right? Well, check every area around that carpet and if you find a Self-destruct/Explosion Trap you WANT to step on it. If Kecleon gets caught in the explosion, he'll take damage and will start going after you as if you stole from his shop. (The thing is, he will be at normal speed! But watch out for the high-leveled power of his!)
It's not necessarily a good glitch though. The following can still happen:
-Getting hurt from the explosion.
-Losing the items within the explosion.
-A voice randomly comes out saying "Help! I've been robbed by a theif!" as if you just stole from Kecleon. (Worse, you don't know where he and his buddies will appear.)
It isn't the best glitch ever, but a glitch is a glitch, right? Give it a try sometime! It's fun to do if you're curious! ^_^