Went to the wrong funeral once, but it was on the right day. A friend of DW's grandfather passed, and we were going the the funeral home for the traditional Jewish funeral. We got a little lost, and wound up about 15 minutes late. We ducked in, sat in the back and ended up waiting a little while, since it hadn't started yet, go figure.
So the ceremony starts, a lot of people speaking hebrew, and we haven't seen any of the family my DW knows yet. So eventually, someone gets up to speak, and it turns out to be the deceased's daughter; who was not from DW's friend's family, who begins to speak about her dead departed grandmother!
So by this time, we realize we're in the wrong funeral, but don't want to get up and leave during the funeral. So we satyed to the end, bolted out figuring there was another funeral going on there around the same time, for the right person, and maybe we can catch up. They were already off to the cemetary, so we get in the car, and get stuck in the procession to the cemetary for deceased person grandma. So leaving the parking lot, the procession takes a left, we take a right past the funeral home working directing traffic, and dissapear.
DW's friend and family got a real kick out of the story, and figured granddad would have too, so it was OK.