'Nina Foch', who played John Ritter's mother-in-law in the film, was originally Ritter's acting coach when he was a student at Hollywood High School and he was really nervous when he met up with her again on the set of the movie.
The screenplay was originally adapted with Dudley Moore in mind. However, Moore felt the part was too similar to Elle (1979) and the recently completed Arthur 2: Dans la dèche (1988). Moore declined the role which led to a rift between him and director Blake Edwards.
Raye Hollitt (Lonnie) was the muscular warrior, "Zap", in the late-'80s version of "American Gladiators".
The original title of the script was "11" and it was going to be a sequel to the hit film "10". However, Edwards only got halfway through writing it when he found out or realized Moore would not be returning. So he took what he had, changed the names and continued writing it as an original script.
The most famous scene in the movie is the one most people remember it for, not the story or the cast or the directing. The glow in the dark condom fight scene. It was a simple scene, set up to be a fight scene in the dark. Ritter is confronted by a jealous boyfriend of the woman he's about to sleep with. The entire scene is in the dark except for the condoms and a comical lightsaber-esque battle happens. It's become so popular in the years since the release of the film that this scene can actually be watched on YouTube.