Diaper Snap \ˈdī-pər snap\ noun
1 : an audible pop made by a persons plastic-backed diaper when they make a sudden movement, usually squatting.

Now you know what it is, have you ever experienced it? I wear 24/7 and when it happens to me (unintentionally), I get a laugh out of it. The snap can get loud so you may want to do it in private. Good times.