People don't want to admit it's funny
There seems to be an attitude in regard to this movie that if you were entertained by/enjoyed it or thought it was funny, that you must be an immature stoner who has burned away their brain cells and spends all their free time drinking slurpees in their mom's basement.
I genuinely feel like this is a holier-than-thou thing where people just don't want to admit that it's funny because it gives them a sense of moral/intellectual superiority.
I'm college-educated, in grad school at a prestigious university, and when I've told people that I think this movie is funny, I've been treated like I'm some sort of subhuman, classless imbecile with an IQ of zero. Sorry, I thought this movie was fantastic.
Part of the joke is the fact that they rounded up some of the most well-known and respected actors in Hollywood to do it, but also many of the skits are hilarious. "Homeschooled" and the vending machine child exploitation ads literally had me in tears. It's absurd and rightly so, because that's all it really aims to be. I find it ridiculous that something like Hot Tub Time Machine has a considerably higher rating than something like Movie 43.