Revealing mistake: In Dirk's first sex scene with Amber they are both supposed to be naked except for their shoes. At the end of the scene Amber sits up on the table on which they had sex as a female stage hand wraps her in a robe, and you can see she is wearing black panties.
Factual error: While Dirk and Reed are running from Rahad's house, and trying to get into Dirk's 'Vette, Rahad fires a shotgun at them. One shot hits the driver's window, which shatters, then a shot at the back of the car showers sparks. Corvettes are fiberglass-bodied, and wouldn't spark. After the sparks, there is no damage to the rear bumper cover, which if really hit with a shotgun blast would at least put some holes in the fiberglass.
Continuity mistake: When Dirk, and Reed are buying clothes, they walk up to the wall, and look at a pair of shoes. Reed is on Dirk's right. On the next shot, Reed is on his left.
Factual error: In the scene where Dirk Diggler and Reed Rothchild work in the recording studio to cut their record, Dirk sings a song called "The Touch." However this particular song did not actually come into being until 1985 when Stan Bush wrote and recorded it for use in "Transformers: The Movie."