One of my favorites is “catching” the “son” jerking off.
You catch him, it’s embarrassing for him but gives you the opportunity to have ‘the talk’ with him; how all men do it, proper techniques, and other things that can be done to make it feel even better. You could show him, but it’s got to be kept secret from his mother because she would get upset and you have to hurry because she could be home at any minute.
You can fill in your own blanks, for example, whether he blows you or vice versa, etc.