I'll share mine first.  I was 21, had visited an adult bookstore a number of times but had been too afraid to actually do anything in the maze of viewing booths at the rear of the store.  The one time I'd ventured inside, I practically came in my pants as I saw guys entering booths together.  A world of casual sex right in front of me, but I was too chicken shit to take advantage of it.  

Finally after months of fear - I got the courage to enter the back room and wander into a booth.  I watched a variety of gay porn vids while I nervously worried about what was happening around me.  The floor was covered in cum stains (and some fresh globs of it) which equally grossed me out and made me horny as fuck.  

I saw two fingers come out of the gloryhole on one side of the booth but I had no idea what it meant.  I pretty much bolted right then and there and didn't return for a month or two.

The next time, I went into a booth - pulled down my pants and jerked it to gay porn in full view of a guy that was watching from a neighboring booth.  I felt sexy as fuck (and hell, I was 21 - I was) and fucking loved shooting a load in front of him.  

After this - I was addicted.  I went back multiple times a week to jerk off in front of other guys.  Finally, one quiet Friday afternoon, a dude whispered through the gloryhole "hey, can I come in there with you?".  Hard as a rock but terrified, I told him sure and opened the door.  He was a few years older than me (maybe 25) white and pretty cute.  I said I didn't want to do any touching and he said he didn't either...he just wanted to have me cum on his face. A great arrangement for both of us!

We watched a hardcore gay vid (shit, I think it had fisting or something really extreme if I remember), he got on his knees and I fucking drenched his face.  I'll never forget watching him use his fingers to wipe up every drop and frantically shove them into his mouth.  We basically shared a "hey that was cool!" and I high tailed it out of there.  Not the most impressive first same sex encounter...but I'll always remember it fondly. 

What was your first time with another man?  18+ experiences only, obviously.