I hate it when I go to a restaurant and someone calls me "young lady", and I never know what to say because I don't want to make things awkward (because people always freak out or get embarrassed or whatever) so I just don't say anything. It always seems so out of the blue because I pass most of the time, it's just really annoying.
Does this happen to any of you guys?

What do I say? :/

I'm sorry man, I hate that too. Here's a thread where someone asked this as well and got some good responses.

https://www.susans.org/forums/index.php/topic,87401.msg623700.html#msg623700

I find that out in public it is easier to correct people. Your moment of awkwardness really does only last a moment.

A couple months back I was getting some groceries and the register was having some sort of difficulty so I had to wait awhile. The checker called her manager over and she felt bad because I was waiting and said something to the manager like, "she's been waiting forever". I kind of laughed and just said, I'm not a she. And of course she was like OMG I'm sorry! And I said it was no problem that it's probably the hair (I had it longer and shaggier at the time). So it was really no big deal.

It all depends on my mood too. Sometimes I just let it go and don't bother.