jack slack
You jack it like you're trying to beat your dick to death, then you slack it like you're dead.
'I jacked it so hard I thought my dick was going to die. Then I slack it like I just ran a marathon.'
'He jacked it like it was his enemy. Then he slack it like he was dead.'
'I jack it like I'm trying to kill my penis. Then I slack it like I'm a zombie.'