You've really never had an attractive member of the opposite sex show up and the girls/guys get all competitive? I'm wondering how that's possible, it happened multiple times a week - a day even - to me in high school and college. I guess always being in mixed groups meant it was always subtly in play.
5 dudes chilling is a different dynamic than 3 guys 2 girls. People who keep insisting it's about some weird need for men to be offensive don't seem to have ever observed basic gender dynamics.(not saying you are, other responders)
Maybe this happened when I was 19.
I haven't observed this sort of thing happening in decades.
Note I mentioned high school and college as the time of these interactions.
That being said it just comes more subtle as people get older or alternatively remove themselves from the dating pool.