When Jill and Jimmy are having their make-up sex, we hear Bruce Willis saying "Yipee-ki-yay." This alludes to his famous line in the movie Die Hard (1988).
When Oz (Matthew Perry) wakes up in bed with Jimmy (Bruce Willis), Willis was naked under the blanket. Perry had no idea why he was naked... and reportedly was too afraid to ask.
The tattoo on Jimmy the Tulip's back is the logo of the production company.
The Buttercup girl is played by Bruce Willis's daughter, Tallulah Belle Willis.