A sexual act in which a man climaxes on a woman's upper lip, then styles her mustache in the fashion of Hall of Fame pitcher, Dennis Eckersley.
If the woman does not have sufficient facial hair to accomodate this act, her actual hair may be used. However, a true "Dennis Eckersley" requires the woman have some facial hair.
"Bro, that chick you took home last night was gross!"
"Yeah, but she looked great after I gave her a nasty Dennis Eckersley!"