I used the following excuse for losing to a completely inferior opponent once
"This controller is screwed up. WTF? where did you even find this God-forsaken controller?"
I have no idea where the guy found the controller that convieniently was the only controller available for me, but here are the differences between it and the standard nintendo-brand controllers I usually use:
-The buttons arround the A button had been rotated 90 degrees clockwise. Yes, X was directly under A, Y (which I use to jump) was to A's left, and B was directly above A. So pretty much whenever I wanted to jump, I would use a B move, whenever I wanted to use a B move, nothing happened, and whenever I wanted to use an A move, I would accidentally jump.
-The control stick had only 6 niches for the control stick to go instead of 8,
-the control stick was double the normal size, so you had to slide it twice the distance as normal throwing off my smash attacks. (which were already thrown off by the fact that the c-stick didn't work)
-Apparently this guy's younger brother used this controller, and he ate very greasy potato chips and such while playing, so the controller was very greasy, and all the buttons were sticky and unresponsive.
-the controll stick had no grip on it, it was perfectly smooth. combine that with lots of grease, and I found my finger sliding across it often without even moving it.
-the handles where your hands grip were rectangular prisms (very uncomfortable)
anyway after losing 3 matches in a row (5-stock matches, where I got him to a single life left each time) I had complained enough to have him switch controllers with me. He claimed that which controller you used didn't matter, and that he would still win. The controller he was using was nintendo-brand and extremely good (probably only a few months old). Anyway, I 5-stocked him without getting hit.