I find that I'm less likely to enjoy a movie if I've read a review first. Inevitably, the review will point out some tiny (or major) flaw in the movie, because that's what a good review is supposed to do, and then I find myself watching the movie and looking for that flaw, and then it shows up, and sure enough it's there, and I can't ignore it. I love to read reviews AFTER I watched a movie so I can look at the flaws they found and say, "Yup!" or "Didn't care about that. Loved it anyway!" I know that's the opposite of how reviews are supposed to be used, but the only way to know for SURE is to see it.
That said, without reading any reviews and only seeing trailers, I know I wouldn't enjoy Bad Grandpa. I suppose maybe I would, but the odds against it are staggering, and I don't think I'll take that chance. :^)