If a teamviewer sessions counts as "screenshare", I've got a good one.

The company I'm working for also got an internal video player in the webfrontend of it's product. A customer called in, because the player "stays black", instead of playing his videos. It's a player for a media library of the customer, so it can be any content. A collegue did some trouble shooting, but since the customer was not very experienced in IT they arranged a teamviewer session. At the appointed time, my collegue called the customer and asked him to reproduce the issue, while watching via teamviewer.

When opening the media player, it stayed black indeed, so my collegue asked the customer to try another video. From my desk I heard my collegue say "Oh god, no" (phone muted) pretty loudy and he asked us to come to his place quickly. The customer decided, it would be a good idea to try the video player with gay porn. So we stood there around my collegues desk, watching a hairy man, getting his asshole licked by another an even hairier man for a few secs.

The customer stopped the playback, said "ok, maybe the other file was just broken.", thanked my collegue and the call was over.

We had a few similar cases.