The Class of '89 - S4.E18

Mary tells the kids that she has the hookup to get Run DMC to play at their prom, but the problem is the kids cannot afford the $5000 fee. Dylan takes their money and invests it in a stock, which goes belly-up. They end up losing all of their money and cannot afford to have the prom in a hotel anymore.

Instead, it is held outside 227, much to the kids' displeasure. Both Mary and Dylan go where Run DMC is and dress up as rappers to convince them to come. Dylan succeeds and Run DMC show up to rap at the prom.