I still recal one particularly erotic experience from my early 20s that I think about from time to time. Particularly when I find myself obsessing over big dicks. (which happens from time to time!)  I woke up, all of 22 next to a 30 year old guy I used to see, friend of one of my friends from work at the time... his beautiful mocha colored body stretched out and muscled on my bed.. I hugged myself to his sleeping body. My pale breasts pressed on his dark skin. 

The lift of a sheet and I saw his sleeping cock. He was a big guy, erect something like 10 inches or more! (that's another story, actually.) But here he was, sleeping. Not shriveled but certainly 'travel sized' and all cute and hooded! His genitals were just so nice and fat, piled there on his leg. Just to satisfy my curiosity, this is what I did:

I discovered, in one smooth sucking kiss, that I could fit this guy - his cock and both of his nuts - into my mouth. A mouthful to be sure, but there I was, when he woke up, like a suckerfish!  It was really such simple excitement, feeling him swelling up in my mouth, with very little room left for him... no place to go.. well... He did *expand* back and back and up into my throat.. as I said, I really have no gag reflex at this point! I did a little back then, but kept it in check with concentration on erotic thoughts... I swear I could actually feel the moment the tip of his cock popped out of its hood and began pressing, naked and swelling against my tonsils.  My little experiment ended when the shaft of his cock stiffened to a length that, the tip pressing deep in the back of my throat, caused his nuts to pop out from between my wet lips..plop! Onto my chin. He'd pushed himself out.