Personally my favorites at the ice cream store are the a-holes who abuse the "free tasting" policy.
My local dairy farm offers amazing ice cream in a very tiny parlor-- on summer days it's common to have a line snaking out the door. So after everyone's been waiting in line for 15-20 minutes, it never fails that some cheap-shit jackass (usually with a brood o' brats) has to try a little spoon of every goddamn flavor and hold up the line even longer. (Did I mention that the way the line's set up, you stand in front of the glass case and see all the flavors for at least 10 of those 15 minutes you've been waiting?)
I'm sorry, just take a fucking flavor gamble and if you don't like it, tough shit. Sometimes I seriously wish that all retail establishments were run like the Soup Nazi on Seinfeld.