I don't know how common this is, but I once worked at an office where this was common. It was an HR nightmare and we kept getting in trouble. Lots of waivers were signed. Apparently a lot of startups have a "frat culture". I can't imagine working at a place like that.
Furries (adults who wear animal costumes, some of which have sex while wearing said costumes) are big fans of Tony The Tiger. Tony The Tiger's Twitter account has been getting raunchy messages from horny furries for a long time. Well, Tony The Tiger has officially banned all furries from contacting him via Twitter. Sorry furries, time to go find another mascot to bother.