It may have to do with many of us being virgins.
How about first kiss or encounters with the opposite (or maybe same) sex in general? My first kiss was kind of funny too actually.
edit: it should be noted that 18 minutes is how long the side is and not exclusively "sex time"
... I have had that problem pre-sex before. He was all like 'OMG YOU HAVE BLACK SABBATH RECORDS" and I put one on and the side ended right when shit was about to get serious... so instead I grabbed my iPod and put on Signify
very little is ordinary through the magic of MS Paint art
Was Really Tall Naked Guy actually in the state you drew him in?
No, thank gawd. At least not that I recall...
You wore your shirt the entire time?
Yes!
... it's been hanging on my closet door at my mom's ever since. It's GLITTERY!