For me it's when furry characters use sex toys solo. Dildos, fleshlights, I just don't like seeing it. Vibrators are fine. Fantasy stuff like portals and potions are fine. and anything's fine if used by one on another. I think it's because in fantasy furry land, you don't need sex toys, there are furries for that. Everyone's sexually open and accepted in a neverending orgy. Using a dildo or fleshlight is like a sign that nobody is around willing to fulfil that role for you. You can fuck in public without consequences. You can go somewhere and expect sex. A nightclub, a brothel, a fantastical location like the spirit world... They're so much more exciting than someone fucking himself alone.