That'd be Max Patkin, who was profiled by Steve Wulf for SI back in 1988:

Max Patkin is Dying. No, he has not been placed on irrevocable waivers or anything like that. On this particular summer night, he is dying in the comedic sense. It is warm and drizzly in Gastonia, N.C., and nothing is working for the Clown Prince of Baseball. Not the imitation of a chicken, not the shadowing of the first baseman, not even the countless (actually 24) geysers he sends into the air from his five-toothed mouth. "What a crowd!" Max tells the crowd. "I had more people in my bed last night."

This is a slight exaggeration, not because Max had company in bed the night before, but because there are 47 people in the stands at Sims Park. It seems that the owner of the Gastonia Rangers in the Class A Sally League, a gracious man named Jack Farnsworth, had forgotten that Max was coming and so neglected to promote his appearance. Farnsworth, who made a fortune selling Bibles and who operates one of the few dry ballparks in all of baseball, had recently undergone brain surgery, so you could hardly blame him.

There are a few people laughing at Max's gyrations on this night, but too few for him to hear. So when the public-address announcer, who is about half the age of Max's uniform (the one with the question mark on the back), blows the introduction to the Rock Around the Clock number, Max stalks off the field in a huff. Ever the trouper, he returns to finish off his act and squeezes out a few more chuckles. One of the people laughing hardest is a man who is taking notes behind home plate and who looks like a schoolteacher. He is Joe Frisina, a scout for the Montreal Expos and, in fact, a former schoolteacher. Frisina says. "I've seen Maxie 50 times over the years, and I still laugh."