Never tell your wife that you got your mother-in-law pregnant. (Matsumoto Shoko JUQ-398)

My wife, her parents, and I went on a hot spring trip, but my father-in-law was under a lot of pressure because he wanted to have a grandchild soon. He had abstained from sex for a month before the trip, but he couldn't take his eyes off his mother-in-law's exposed chest. He even lost his temper and sneaked into his mother-in-law's room...