It's such an addicting feeling! Congrats on your first sub. Now you're hooked ya crackhead!
My first ever was a Peruvian necktie but I don't exactly count that. I was on active duty at Moody AFB and I was in the gym smacking the heavy bag. Dude started chatting me up and asked if I trained at all. I said yeah, but only for like two months. He said he'd been training for years and asked if I wanted to roll. I said sure why not. He shot for what I now recognize as a laughable double leg and BOOM it was right there. Caught him in it again a few minutes later. I decided he was full of more shit than a manure cart and quit rolling with anyone outside of a legit gym.
My first real submission at Roch was Invisible Collar. It's been my absolute favorite ever since and I work on it regularly.