Many years ago I saw a great Cub fan slam in the form of a sign held up by a White Sox fan. The Sox were hot at the time, (young Frank Thomas era) and Comiskey was suddenly filling up with bandwagoners.
Some classic, stereotype Chicagoan (he looked like one of the Saturday Night Live "Ditka" sketch characters) held up a sign for a camera that said "Yuppie Scum! Go back to Wrigley!"
