Back when I taught diving, during the first classroom session, I would tell my students to close both their eyes and then press in on their eyeballs with their fingers for 4 seconds and then stop.... I would then say to them, did anyone damage their eyes or injure themselves? This always resulted in puzzled looks and an answer of "nooooooo".
I would then explain that I didn't expect them to injure their eyes, because they all know that they are sensitive and would feel pain or even cause damage if they pushed too hard....and the looks I would get.. would be like... do you think we are retarded??? What the hell was THAT for?
I would use this stupid little exercise as an introduction to ear equalization and tell them that THEY were responsible for THEIR OWN ears.. That they are delicate and easily injured, (just like your eyeballs) and there is no way that I will ever be able to tell how much pressure they are putting on their ears (or their eyes). I would explain that equalization should not hurt at all and that ear injuries are probably the most frequent injury that divers experience.
The whole exercise is useful to get across the idea that you do not play games with seeing how far you can go without equalizing, any more than you see how hard you can press your eyeballs back into your skull.