Not long after I turned 18, my family went on a short trip to Disneyland/California Adventure (we used the "Park Hopper" pass). I was still in that sort of oh-my-god-I'm-an-adult-now giddiness, so what better way to celebrate it than with a bunch of kiddie rides? I should also note that I'm always told that I look several years older than I actually am (in ways ranging from, "A freshman? I thought you were a senior," to, "Did you know that you look EXACTLY like your mother?"). I don't have a kiddie face/build/height at all.
Anyway, in the midst of "park hopping," we stopped for lunch at an Italian restaurant in the Napa Valley section of the California Adventure park. Our waitress was friendly and courteous. As she seated us, however, she turned to me and asked (in the patronizing sort of voice one would use with a child, not just the usual fake-perky-customer-service voice): "And do you need a children's menu?" I was utterly surprised, but stammered out that a regular menu would be fine.
Yes, she was a good waitress and I didn't hold the incident against her; no, I wasn't rude to her about it; yes, she got a good tip. But my freshly 18-year-old ego took a great blow that day.