Story time:
This happened about 12 years ago. One of my best friends got engaged to his high school sweetheart. The two were made for each other - both nerdy / quirky in the exact same way, really sweet, etcetera, etcetera.
Anyways, my friend's fiance had a sister, Cadence. Cadence was gorgeous - beautiful light red hair, awesome body and a personality to match. Me and her started hitting it off really well, and by the time the day of the wedding came it was pretty clear we were going to have a lot of fun together.
Before the ceremony officially started, she came up to me a little tipsy and whispered in my ear to meet her in a room away from all the other guests. Holy. Shit. I was ecstatic.
When the time came (and after a few drinks myself), I went into the room. It was really dark but I found her pretty quickly. Things began to escalate, me feeling her up, her feeling me up, clothes coming off - you know how it is.
Anyways, it turns out this private room wasn't so... private. Two of my buddies who were looking for me opened the door and found me in all my glory. At first I was more proud than embarrassed to be honest. That is, until I looked back to Cadence and realized it wasn't Cadence, but her GRANDMOTHER! Christ, this woman must've been at least 40 years older than me. I freaked out, my buddies immediately slammed the door shut, and I just got my clothes together and bolted as quickly as I could, the entire time this woman yelling at me to continue! Jesus. The worst part was, the entire rest of the wedding this grandma kept trying to subtly flirt with me - so god damn awkward.
Worse yet, one of my friends ended up banging my mom after the reception. I mean, talk about a real American wedding.