The dry dogwood happens when a man over the age of 70 tries to engage in intercourse. Whilst about to cum he pulls out and tries to ejaculate on her face only to see a cloud of chalky dust come out accompanied by the short burst of air much like that of popping an innertube. Upon spreading this powder on his parteners face, he must then yelp out with possibly his last dying breath "dry dogwood!" to complete the act.
Dude, yesterday I thought my grandma was doing drywall work but it turns out gramps just gave her the ol' dry dogwood