In order to be able to jerk off, you need to get it up.
"Schlappschwänze" means literally "limp-tails", where "tails" is a euphemism for the penis, so if you want a better translation it's "limp dicks".
"Schlappschwänze" means literally "limp-tails", where "tails" is a euphemism for the penis, so if you want a better translation it's "limp dicks".