Way to keep it classy Incline... pretty sure THAT comment should be flagged as abusive by the site moderators. That's in the job description, right?
I believe the professional description would be business casual dress for such a work-related outing. Maybe even dressy causal if it's less formal & more social than business.
Sad truth is, with co-workers like Incline around, it's safer/smarter for us female Nuke workers to NOT attend social outings like this dinner. All it takes is a a few too many Good Ol' Boy whisky drinks for jack wagons like him to get too friendly & forget you're a CO-WORKER.
Good luck & make sure to leave long before the 3rd round of drinks. That little secret will preserve your sanity & professional reputation.