That Smell is a Lynyrd Skynyrd tune that is about drugs and the first line in it is about how Gary Rossington crashed has 76 Ford Torino into an oak tree along Mandarin Rd in Jacksonville, FL. This version Marty complained about the smell because he didn't use up his diaper but his skunk friend (Chad Farnswick) did.

Marty: It stinks in here, and I Know I didn't use up my diaper