I love how Cracked.com summed it all up
"In The Guilt Trip, Barbra Streisand and Seth Rogen trade penis jokes and try to out-guffaw each other for two irritating hours that no one would ever exchange money for. Going to see it would be like putting on 3-D glasses and chewing open the Hellraiser puzzle box. It was never meant for the world of the living, and should be placed gently back into its coffin of spiders and buried beneath the roots of a dead oak tree in a bleak Romanian forest."