one off the wrist
It is, indeed, yet another euphemism for masturbation.
As the description suggests, it generally refers to male masturbation.
Synonyms for one off the wrist
On this page, you will find 30 slang terms related to one off the wrist. Some of the top words include: me-time, kitten killing, Playing with the dirty sock, roughing up the suspect, rosie palms, and 25 more.