Dam Wife and Dark Wishes Wish It Went Further Downhill. (It's a Water Pun!)

Listen up, dum-dum. You see, the joke plays on the double meaning of "flow down." The dude saw his wife at the dam, which is a structure that stops water. He wanted his wife to "flow down," which sounds like he wanted her to go further down the river, but he actually wanted her to, uh, meet an untimely demise by going over the dam. Get it now, blockhead?