Full Brimley
A very full and hard penile erection - derived from the scene in the movie "Cocoon" where Wilford Brimley's character in describing his boner to Don Ameche (after swimming in the "magic" pool) says, "A cat couldn't scratch it"
"I swear to God, when Tina walked out in her yoga pants and sports bra, my business went Full Brimley"