punch (someone or something) on (something)
To hit someone or something with one's fist on a particular spot or part. I punched him right on the nose for saying such offensive things. He punched the cabinet on the top part of the door to get it open.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
punch someone on something
to strike someone on some body part, typically the shoulder. (Not with the intention of causing harm.) Sally punched Frank on the shoulder just to show they were still friends. Tom punched Fred on the shoulder in a friendly way.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.