I have "caught" an ex mid flow numerous times but it was intentional even if never said, with an invite to join the fun. She always wanted me to finish with the vibe as she reckoned the vibrations in her hand were to distracting to enjoy fully..
More funny than anything was going home with a sort of friend with benefits. I sprawled across the bed, fully clothed having just got in, stretched so my arm swept under one of the pillows only to find a damn big vibrator. I just held it up with a grin and she sn*tched it off me and hid it. I'd did hit the on button first but it vibrated for a second and died so I gave plenty of teasing about the amount of use it got if the batteries were dead...maybe thats why she had me home with her that evening
. Later on while having fun I pulled her hand down and she got herself off. That must have been a big turn on for her as she had the most intense and long orgasm that i saw with her and as her 'secret' was out why not. We wasnt really good friends and probably added to her sense of naughtiness.