The best one I ever had was during a gig with my old jazz-fusion trio at a jazz venue in Bristol. We had just finished a John Scofield tune and were about to launch into another instrumental epic when this pissed student-type came up to me. "Do you do Iron Man by Black Sabbath?" he asked. I looked at him incredulously. "Do we sound like the sort of band that does Iron Man by Black Sabbath?" I replied with a grin. We launched into the aforementioned instrumental epic, at the end of which there he was again.
"Do you [i]know[/i] Iron Man by Black Sabbath?" he asked. "No we bloody don't" I replied somewhat testily. I wandered away from him to try to signal that the exchange was definitely over and we launched into a Brand X tune.
At the end, yup, there he was again. "Why won't you play Iron Man?" he demanded. I gave him my very best Paddington Bear Stare. "Oh come on, you [i]must[/i] know it!" he said. "Look mate," I said in a firm this-conversation-is-over tone, "just f*** off eh?". (I wouldn't normally tell a punter to sex-&-travel, but this gimboid was seriously getting on my toot.)
Thankfully, he got the message and f***ed off.