Idioms

jump all over someone: severely criticize / find fault with someone.

A: "What's wrong with Joe?"
B: "He's feeling bad because his boss jumped all over him this morning."

jump the gun: do something before it's time to do it.

A: "How did Marsha know about the party? It was supposed to be a surprise."
B: "Chuck jumped the gun. Without thinking, he said, 'I'm bringing the cake at your party;
I hope you like it!"

jump to conclusions: decide something too quickly and without thinking about it or
considering all the facts.

A: "Angela just doesn't like me. She won't even say hello."
B: "You're jumping to conclusions. Actually, she's very shy."

junk mail: unsolicited mail (usually advertisements for something you're not interested in).

"I didn't have any letters today--only junk mail."