The OP used the word menu, was it a menu or a signboard?
A menu is a lot harder to modify. Need to reprint them with new prices usually at a professional shop etc etc. A signboard at least they could put a new price over top of the old price. I suppose you could do that with menus but if you have like 100 of them...
Maybe he could have put a sign on the counter, all prices +10%. He probably could have done a lot of things, at the end of the day we're here talking about $1.25 and the OP feels ripped off, over $1.25, and making a post here about rather than just discussing it with the owner at the time.
As I said earlier to me it would make no difference if the pizza was $16.75 or $18 because I would have just given them a 20 and called it a day in either case.