"Shit Liberals Say or Do" is a long and cumbersome name for a forum. "Shit Liberals Say" is much more to the point. The "or do" part is implied; if anyone doesn't understand that, a message could be put in the sidebar stating that the forum is not just for stupid things that liberals say, but also stupid things they do.
The same goes for /f/ShitRedditSaysOrDoes.
yaaqov wrote
What about just /f/shitliberalsdo? "doing" definitionally encompasses "saying", so it's clear from the title itself. I also happen to think it sounds sliiiightly better, maybe because the /z/ sound that ends "liberals" doesn't have to border the /s/ sound that begins "say"; the string /...zs.../ is a tad tricky to pronounce.