I don't see the characters as dull, and they are clearly not that ordinary as they are roleplaying in a laundrette. By plain I mean of course they will have their unusual quirks like we all do, but I don't think this is the type of film to explore them?
It may just be my inexperience of writing films, as like I said this is my first attempt. It was a challenging script to write because they are essentially four characters. What I wanted to do was start the film with the audience thinking we are being introduced to two people who haven't met before. It is Steve's reluctance to hold a conversation which is a bit puzzling (as most men would in this situation). It's about Lexi not having control over the man (which she is used to) and when she shows her cleavage that's when things pick up.
In the warehouse scene, I wanted the audience to be shocked how the film had changed pace. By the point the watch goes off and the mood changes I feel the characters covered enough of their history to clue the audience up. Lexi mentions their marriage, and I think clues like this are enough to add depth. Just out of interest, how would you develop the characters?
For the record, I do own a fluorescent tutu.