Brian Benben (I think) - "Clean and Sober" - 1988

 Michael Keaton does it right. His friend gets up and goes into another room to change clothes, so what does Michael do? He waits till his friend is stripped down to his undies and then walks in on him uninvited.

Christian Maelen - "I Think I Do" - 1997

Reader suggestion.

Thom Bierdz - Youtube

Not sure what these are from ....

This one seems separate from the others .. no facial hair or tattoo.

Cory Faucher - "One on One" - 1977

Decent 70s Robby Benson sports vehicle. His roommate (Cory) spent some time alone with Robby in his tighty whities. Scene is a little dark. This is the only acting credit Cory has.

Jay North - "The Teacher" - 1974

"Dennis the Menace" all grown up. Unfortunately it was filmed in almost total darkness.

Bodie Olmos - Battlestar Galactica (update)

Have to admit I never watched this series so thanks to reader who pointed out the scene. Wouldn't have expected tighty whities to show up in a futuristic show! Not the greatest caps but the best I could do.

Sebastien Guy - "The Model Solution" - 2002

Speedo and Tighty whities

College students showing off (reader submission):