My Girlfriend's Mother 2.

Young Se-hee gets married to middle aged Min-goo, but she's not happy with his 'item' as he's old. While she goes on vacation with her husband, Min-goo's daughter Yoo-jin calls her boyfriend Ji-hoon to the house when her parents are not there and they have sex. Meanwhile, Se-hee comes back home early from the vacation because her husband has to work and runs into a completely naked Ji-hoon.