If you walk around your place of business - an office, warehouse, studio, wherever you work, is it unprofessional to be sporting hickey(s) on your neck?
This does not apply to people who work from home, or work alone (in either case you are lucky)
It's unprofessional to give or receive a hickey during work hours. (Especially same sex hickeys, never an appropriate time for them!)
But if you have gotten one away from work, wear a Turtle Neck, or tie (For the guys.)