Still if you ever hang out with simpler people (e.g. what in the UK is called a flat roof pub ) it is typically the 80 IQ guy who insists on fighting some other guy for no good reason whatsoever and it is the 100 IQ friend who is telling him don't be an idiot he is twice your size and did time for stabbing someone. Or you see how dumber criminals get busted on really trivial mistakes - if all you have is tribal customs instead of laws it probably still works the same way. Or, maybe, the difference between a 80 IQ and 100 IQ tribal warrior is largely that the later does not think "we are the awesomest" is a good enough reason to attack a tribe that has three times as many warriors. In short, while really high IQ does not help with reproduction much, really low IQ provides excellent opportunities to shoot oneself in the foot in a competitive social environment. What we today consider average IQ simply translates to a hominid who is a bit cautious and can assess when to be brave and when to be a coward.

Note that none of your examples are cases of sexual selection.

While the dumbass having 4 kids with 4 different single moms is a popular trope, in really the really dumb guys tend to go in and out of prison

Those don't necessarily interfere with each other.

Sure, a peacock having a REALLY huge tail may be detrimental to its reproductive success because it cannot even go through a mating dance routine maybe,

A REALLY huge tail is detrimental because it makes the peacock more likely to be eaten by a tiger, i.e., non-sexual selection. If peacocks were placed in an environment without tigers females would chose even larger tails. Heck they've done experiments where they glued on extra tail feathers to give a lucky peacock an even larger tail, the result being that females preferred those males to any males with a natural tail.

Heck consider an actual example of sexual selection in humans: Men like women with large breasts. Notice how common ridiculously large breasted women are in everything from advertizing to anime to video games. Heck in ancient times people would worship multi-breasted fertility goddesses. Contrast that with the portrayal of smart men, who must be given an actual "sexy" trait (like being rich or a badass) for women to accept them as "sexy". For example, Q's gadgets contribute to James Bond's (not Q's) sex appeal even though he's not the one developing them.