In college, one roommate was known to bring a lot of ladies home of lower quality. So the rest of us roommates printed up a fake letter from a real law firm with a real phone number for him to call to schedule a paternity test, put it in an envelope, made it look like it came in the mail, and put it with the rest of the daily mail. We knew when he got back from class so we all sat in the living room waiting....our assumption was he would either a) immediately go "guys wtf look what I got" and we'd all have a good laugh then tell him it was fake or b) he would call the law firm and they would tell him they don't know what the eff he is talking about so then he would figure it was 4/1.
Well c) happened where he didn't call and didn't tell any of us for like all day....so we started freaking out that he would do something irrational so we had to tell him....he wasn't too happy with us. We felt bad after that :(