thickening up
The arousal of a man's penis. To begin to become erect. The progression from flacid penis to semi to erect.
Yorkshireman, "God, I wish those lambs would stop frolicking about in that field. I'm thickening up."

Scouser, "I love orange girls in shellsuits. I'm thickening up."

Brighton man, "God I love it when he wears those pants with the arse cut out. I'm thickening up."

Essex Man, "Jesus, that Burberry bra and G-string really do it for me Sandra. I'm thickening up innit.

Wiganer, "Bloody hell, look at the pastry on that meat and potato pie, I'm thickening up."

Gorby, "Look. At. Mi. Sister. I'm. Tricketing. I. Mean. Thick. En. Ing. Up."