Awesome if you perform, when it's you and a mate of yours fucking a girl. I've done this. We were both similar in dick size (above average, nothing colossal) and body (between thin and non-steroid muscular). Lass was a proper slag, mind. I don't think I could do a thereesome with a dude with a much bigger cock than mine. And I'm quite good at the art of sex.

A delight if the 2 lasses you're gonna fuck are willing and prepared for it (their idea), because the best thing imaginable happens and both girls are jealous and want to be the favourite one. And it's a 2 on 1, you're the one.
I was in a sexual relationship with one really nutty lass who was a tattoo artist, and she eventually called in an acquaintance of hers.
I dodged a few bullets with this one. A lot of my first time experiences experiences happened with her: rimming, fucked up dress-up fantasies, golden showers (properly done, which tells us everything you need to know about this lass' sex drive), anal done weekly (with not even one smear of shit on my penis) and all sorts of sexual stuff in public.

The most hilarious thing is how I was so happy with having fucked 2 girls and at the same time that i actually phoned my late dad a day after, and ended up being berated and actually told to go get a test for std's. Lol.
RIP dad.

I'd never agree to one if i have feelings for one of the girls. There is way too much shit happening.