Embarassing moments with aleatório people?

I was at the mall one dia with my mom, and she saw one of the ladies she used to work with 15 years ago, so they stopped and said their hellos and all that. My mom mentioned that I had just graduated from high school the night before, and the lady was like "Oh congratulations! From which school?" I said the name of my school and she was like "Oh yeah they're our rivals we dont like them blah blah blah". But she was just playing around, so she made that 'Oh Im just joking with you' gesture with her hand [or wrist, I guess], and I thought she was giving me a high 5 so I put my hand up to her hand, but it just looked like I was pushing her away and like I didn't want her to touch or come near me...
I felt soooo awkward just standing there while they continued to talk to each other, I was so embarassed! Her daughter was standing across from me looking at me all weird and stuff I was thinking oh my gosh.... I felt so dumb! I guess I could have said "I thought you were giving me a high five" but that probably would have made things even mais awkward. But I laugh about it now :]

So have you had any embarassing moments with aleatório people or people you don't really know?
<3