Often in a political context, the term “the many not the few” is used in campaigns, focussing on the large majority of the typically underprivileged population; instead of the elite few, who often oppress them.
So, “for the manydem”, essentially means the same thing - and of course is a play on words - but referring to a subset of this population known as the mandem
Mandem 1: Hey bro that ain’t no regular graph
Mandem 2: Yeah man, it looks more like art
Mandem 1: Low that shit.......but wait it says “for the manydem” are they talking about us cuz?!
Mandem 2: well for real, we da mandem