Why would my ex-boyfriend keep my "toy"?

We were together for about 2.5 yrs. Things wer getting serious when he decided to break things off so he could pursue other options. I practically lived with him so when we broke up I had a lot of stuff at his place. He has given almost everything back except for this vibrator. Why would he keep it? And, I know he didn't just forgete to give it back. He knows he has it.