I had a pretty good one occur... let's see if I can remember it...
I was racing against a single opponent, near the end of the difinitive final track (we were both Yoshi, by the way).
I was in a narrow lead, but then he got a blue shell. I tried to stay close to him so that he wouldn't get a chance to use it. I slowed down considerably. So did he, until we were both stopped, frozen at a tactical impasse. I drove forward a bit, and he backwards, then we revesred directions. We went back and forth like this for a bit, occasionally hitting each other, laughing the whole time (well, I was laughing; I can only assume he was, too), until I finally had to relinquish the win.