About a year ago, my husband, my two sisters, my great-aunt, and I went out to a locally-owned restaurant in Rochester, MN. We started to order drinks; it got around to me, and I ordered a margarita. I didn't have my ID with me - we were on a trip and I had lost it the day before we left, and I wasn't driving anyway. My husband is 12 years older than me, and if he's with me when I order drinks, I almost never get carded, so I figured I'd try it. Of course, the server asked for my ID, and I explained that I didn't have it, but I wouldn't mind getting a Coke instead.
He says, "Oh, no, no, don't worry about it; I think it'll be okay. Are these your parents?" *indicating my husband and my great-aunt*
Okay, my husband is way older than me, but he doesn't look old enough to be my dad. My great-aunt is in her seventies - she looks waaaay too old to be my mom. And no logical person would ever, ever assume they were a couple.
I was highly amused, and my husband was mortified. I got my margarita, even though he probably shouldn't have served me. He didn't get a great tip, but it wasn't just that one flub - he screwed up the drinks, we had to ask repeatedly for refills, ketchup, etc, and he kept hanging around trying to flirt with my sisters and making conversation difficult.