"Jerk" comes from the phrase "Jerking Off" which also means masturbating "able" means having the ability to do something/opportunity do something
Combine them together and you have "Jerkable"
In simpler words, Jerkable means being able to jerk off to something.
Joon Sung Kim: "Bro I jerked off to Hentai yesterday, that shit was awesome"
Aiden Lee: "Hentai??!! wtf man! that shit is unjerkable, how do you jerk off to animated characters"
OR
Aiden Lee: "bro did u see that Ash Kaashh gawk gawk video?"
Joshua Hwang: "Yeah man, that shit is jerkable as FUCK"
Similar to "Carpal Tunnel Syndrome": pain, tingling, and other problems in your hand because of pressure on the median nerve in your wrist. Caused by excessive jerking-off.