Hammer-pouch is a colorful slang term for scrotum used by Lenny, and others. He calls his testicles 'hammers'. Rosie used to kick his hammers in his hammer-pouch when he tried to get too close to her.
Trivia[]
This interesting use of the word hammer may be another nod to the original series in which hammers were the iconic symbol of the Hammerite order (and to a lesser extent the Mechanists).