faplock

A slang term for the condition your wrist experiences during a lengthy masturbation session, especially when stroking very fast. When someone has not waited out the refractory period (the duration of time between masturbation sessions when you cannot achieve full erection), you are likely to try too hard to have another climax and end up in a condition of faplock.

Faplock presents as a numbing or burning sensation in your wrist which will prompt you to either switch hands, or wait for a time for the pain to pass. Medically, it is a buildup of lactic acid in your wrist muscles which causes them to temporarily give out, disrupting your masturbation session.

Fap is the slang term used as a sound effect to indicate the sound made during masturbation, popularized and primarily used in Japanese comics.