Downing

Downing is essentially looking down from a height into a girls' shirt/bra to look at her breasts.
Term was probably made up in "Bill and Teds' bogus journey" during the Seance scene when the pair looks' down Missys shirt.

Guy 1 "Dude, We're you downing Stacy today?"
Guy 2 "Yeah, I can confirm those breasts are sweet as FUCK."