I have been jealous of a friends sex life before, it’s a guy I know really well who also happens to be really well hung.
We met at work, he joined the company a few years after me, when he first moved here he was single so lived in a shared house (just like I did in my first year).
He very quickly ended up shagging one of his female housemates who of course discovered he was hung like a donkey, and she promptly told the rest of the house. Over the next month or so he’d ended up shagging all 3 of his housemates, including one who just couldn’t get enough of him. The last week before they all went their separate ways it was just him and her left in the house and he pretty much destroyed her in every room on a daily basis.
I crashed at his house one night after a few beers in town, I slept on the sofa and I could hear them going at it in his bedroom above for most of the night. The next morning I was taking the piss out of him (and letting him know just how much of a lucky bastard he was).
So not really jealous of his big cock, but I’d not have minded getting half the action he was having in those few weeks.