I am 36 and I caught my stepson stealing used thongs from laundry [MF]

I have read stories and watched videos of this happen but never thought this would happen to me.
After my gym I threw my used thongs in the laundry and after shower as I was coming out, I saw my stepson stuffing my thong in his pocket and rushing out of the room. Upon checking my collection, I’ve 14 silk and satin thongs missing.
Any guesses what he got for Christmas this year?