The word ‘enjoy’ nor the words ‘enjoy yourself’ mean or insinuate masturbation, just an fyi… enjoy is probably a slightly more formal word though… ‘did you enjoy yourself’ does not mean ‘did you masturbate’…. Just saying… you can be having fun and making fun of your friend to imply it…. But it would be a stretch.

…. “Oh yea, you were having fun relaxing in your room all night doing nothing? Did you enjoy yourself?”… even this would not insinuate masturbation, but it could if you and your friend had some dynamic where you were regularly making fun of each other for sexual reasons (you would need some other context, like a stroking motion with your hand while you said it)…. Or, if I was your roommate, and you just teased me for my girlfriend or boyfriend yelling and moaning while we made love, and I said, “oh, you were in your room… don’t lie, you enjoyed yourself.” Maybe then, but even if this case, you would have to be the one implying that you masturbated while the roommate was making noise, “oh don’t worry about the noise last night, I absolutely enjoyed myself.”

If you are over using the word ‘enjoy’ and using pitch and other inflections with it, I could see how someone could think you were being a little creepy. “Did you ENjoy yourself? No really, did you enJoy it?” If you overuse the word it could seem a little odd.

Instead, try, ‘that sounds cool’ ‘super fun’, ‘sounds nice’ etc…. ‘You had a good time?’