Yeah happened to me once with my step dad. He saw my erection and said oh you like it you little p**** and gave me additional straps. Personally I feel he enjoyed humiliating me and pulling my underwear down.
When he took off his belt I better necked quite , worse someone watching but less duration and intensity. No wonder turned on when I'm only person not wearing clothes. Permission to get dressed when sent to my bedroom like grounded or showing report cards protocol. Still Jack off to this and videos like this sceen