Ya, not hating on all girls, but some just don't have common sense.
One of my friends (who is a girl) has never understood a joke anyone has told her in like her entire life.
She just can't put it together and understand the humor. And she isn't challenged, she is smart, aperantly, she gets 80's.
Though, there are some guys who are dumb as shit. But it depends who you talk to.
To conclude, I don't think society as a whole is getting dumber, it's just that there are more people who have no common sense. Not everyone, just more cases of dumb people. There are still many smart people, and they are getting smarter, but the dumb people are getting dumber, so it's more noticeable.
END RANT