Continuity mistake: When Ren is dancing at the drive in, he starts dancing with a girl then stops to watch her. When he starts dancing again he moves slightly in front of her in the shot. Then in the next shot they are side by side.
Continuity mistake: When Ren and Ariel join Willard and Rusty in fighting Chuck and his friends, Chuck says to Ren "Why don't you come down here." As he says this he makes a "Come over here" gesture with his hand. The shot is from behind him, but then when it switches in front of him his hand is already down by his side before he put it down in the previous shot.
Continuity mistake: When the main characters are dancing at the drive in, Ren makes his way over to Ariel and dances while she is leaning on a car hood. When he gets to her the shot shows what's behind him (slightly at an angle) we see Chuck sitting up on his truck bed. When the shot changes to show his reaction he is leaning back, then sits up.
Continuity mistake: Toward the end of the movie, at the big dance, Ren and Willard end up outside for a big fight with Ariel's ex. They get dirty, but when they come back inside they are in clean suits.