If it's any consolation, I don't think it's that unusual to feel that way. My DD is still trying to decide about junior prom, but there's a good chance she and her friends will choose to do what they call "anti-prom"- basically, getting together on their own. It may involve dressing up or not, and will probably involve eating out, but otherwise it's doing things they enjoy together, where they can talk to each other, and not have to deal with all the annoying/hassle parts (and people) associated with prom. I think it takes some maturity and confidence to buck the tradition- there is a lot of pressure, both from peers and adults, too.
Personally, I went to my prom and senior ball, but in retrospect, would have been happier doing something else. Maybe now that he's seen what it is, he can make different (or more informed) choices, And honestly, you never know, kids change a lot during this time period- it's possible he might enjoy it next time!
