Maybe it's just a regional thing? Perhaps I'm showing my age? But us old Yankees either went to the prom or we didn't. Right Larry David?
Seriously folks no one says, I'm going to Super Bowl, or I'm going to Macy's Thanksgiving Day Parade, both of which are pretty iconic events if you ask me. It's just so weird and wacky that the prom, of all thangs, gets the grand distinction of the dropped pronoun. Anywho, I got to get in car, go to grocery store and bank, and later tonight I have dinner date.