A woman on whom backside attack is impossible due to bulkiness. The hindrance resulting is a case of too much cushin for the pushin. So named for inability of a tertiary alkyl halide to undergo the Sn2 reaction.
Guy: Oh man, Oprah is so fine. I'd doggie on that all day.
OtherGuy: Dude, you never could, she's a total t-butyl.