Corrected entry: When Marty is recovering from being hit by the car, his mom continually refers to him as Calvin. When Marty asks why, she responds "Well thats your name isn't it? Calvin Klein. It's written all over your underwear." But when Marty puts his pants on, we see his purple underwear and there is nothing written on them.
Gavin Jackson
13th May 2006
Correction: The writing is on the waistband of the underwear which is covered by Marty's shirt. If you watch in slow-mo Marty lifts part of his shirt for a split second and you can see something written on them.
Mister Ed