When you genuinely get along with the folks
You're supposed to like the in-laws, but do you really? Even if you don't love them, any effort you put in with our folks is a turn-on for any man. Mom carries a lot of weight in men's relationships (like Dad does in yours), so any effort will ultimately be rewarded.
Whether you help them out by chopping vegetables before dinner, set the table, or merely visit them without us is so incredibly attractive because you're making an effort with us, but more importantly, with two of the most influential people in our lives.