S06E17: Happy Jack

Donna catches Eric 'taking care of business' in her bathroom and is completely horrified. Afterwards, Eric's friends and family tease him mercilessly and Donna can't even look him in the eye. Amazingly, Eric actually manages to make this embarrassing situation worse when Donna finds out what brought on his need. Meanwhile, Kelso, now calling himself "Mike" and sporting a moustache, goes on a major maturity kick, so Hyde and Fez decide to knock him down a peg or two.