I found the link to this buried in the middle of the Shay drama on
shiroioji's LJ on page 8 or so. Of course, it's not probably an average first time for buttsex, but it's a journey into TMI that the slash/yaoi writers (or het or yuri writers) that have every single one of their first time buttsex fics turn out perfectly need to read.
SO NWS and vomit-inducing, but informative in a TMI trainwrecky kind of way