For me, the biggest issue I've encountered is in the seating process. The "wouldn't you rather sit at the bar" even though half the place is empty, the sticking the solo diner at the worst table in the restaurant, etc. I've started to take note and never return to places that do that - even if I'm eating with someone else.

I've rarely experienced an issue once I actually get seated (the few places it has happened are also on my never visit again list).