My sister is 3 years younger than me. She invited me to her graduation weekend at Sienna. Well, she had this smokin hot roommate who I had hung out with on several occasions when my sister brought her home with her. Nothing ever happened between us, but we were always flirting with each other. Long story short...the night before graduation we all went out and got really, really messed up. I don't remember much of the evening, but my sister told me later that I was all over her friend at the bar and they found us fooling around in the parking lot. She was pissed. The next morning I woke up to my sister screaming at me at the top of her lungs. I was wrapped up, naked as a jay bird, in a blanket with her BFF on their kitchen floor. All her roommates came running to see what was happening. Let's just say my sister didn't speak to me for a few days, and my parents were not impressed. I was young and single and she was more than willing...what's a guy to do?
What was really awkward was when the same girl was maid of honor in my sister's wedding (about 10 years later) and I was a groomsman...with my very pregnant wife sitting just a few yards away from us.