jack around [possibly offensive]: waste time.
"Will you please stop jacking around?"
jam, in a (1): trouble.
"If you're in a jam, I promise to help you."
jam (2): improvise (musically).
"I'd love to jam with Bon Jovi!"
jamming, to be : going well.
"Dave's ESL Cafe is really jamming!"
jerk: stupid or annoying person.
"How could you go out with such a jerk?"
jillion: an immense number.
"Do you really have a jillion problems?"
jock: someone good at sports.
"I've never been much of a jock."
"Where's the john?"