Sad proofing is a process that occurs after a friend breaks up with their boyfriend/ girlfriend. It consists of removing all artifacts of the relationship and placing in them in a box that is hidden from said friend. Sad proofing is done in order to keep the recently heart broken person from sitting around being sad.
Jim: "Yeah, I had to sad proof John's room last night after I found him weeping in bed with a bunch of pictures of his girlfriend all over his room."
Steve "I did the same thing for my friend the other day. Ever break up needs a good ol' sad proofing session"