Whatever you want. However, I recommend to switch to PJs after "dinner" and switch back before landing. You won't feel rotten being still in the same clothes when you get to your destination. Plus, you'll be able to sleep better and enjoy the BF seat. Ignore what other passengers in the cabin think, BTW. (I bet those are first-timers or op-ups.)

I've done this before wearing a suit (for a business trip) and also dressing ghetto (during leisure trips).