A day for a good old fashioned dry hump. Lie on top of someone, anyone will do, and rub against them suggestively. Moan a lot. Make promises you don't mean. Lie. Do this in your office or in an elevator. What the hell. Then go and change your underwear.
I did the hump on hump day.
I humped old Humphrey on hump day.
Mike humped Louise about 30 years ago and always regretted it.