AFAIK, bunny ears is just a photo thing. Like photos with telegraph poles coming out of your head, or powerlines hanging from your ears, or propping up the Leaning Tower of Pisa, it's one of those silly photo-illusion things. Not that I'm an expert, but when me or anyone I know has done it, it's always a general fooling-around thing.

In answer to your question, consider another question "I just stuck a sign saying 'kick me' on someone's back, why are they annoyed at me?" If you're making them look silly, and if they've not got much of a sense of humour, there's a good chance they will get annoyed by it, no?

Graham.