How can people be so stupid?
It's just "so's," the rest of the sentence is correct in grammar and spelling. Sure, not exactly essay language, but acceptable in speech. (Unless one is in a region where "so's" isn't used. Then it's just sort of dumb.)
If you're going to say "so's," you might as well add "Ah kin tek perkawshuns."
I have heard "so's" used by teacher, and not dumb ones either. It's definitely a regional thing and doesn't make the user an idiot.
It's regional and bad english. WE MUST DESTROY BAD GRAMMAR! WWWAAAAAAAARRRRHHHH
Wot da hell is you lot on abowt mon!