Vaginas definitely do come in all shapes and sizes, and if the joke was meant to be about that I would have found it funnier. But for me, it came across as an attempt from the youngest member of the team to "relate" to or bond with the burly, masculine men by trying his hand (awkwardly) at misogynistic locker-room talk. I just found it to be rude and dated, but I don't begrudge anyone who found those jokes funny out of context.

To be fair, I wasn't the target audience for that joke or for the first half of the film's genre anyway. The male bonding stuff was probably really important for post-Vietnam vets and American "bro culture" in the 80s, but it isn't my cup of tea. I prefer sci-fi that's a little more sophisticated.