Playing golf with clients is one way to 'mix business with pleasure'. [=to do something enjoyable that is related to your work]
I accidentally 'mixed up' the two files. [=I put each of the files in the place where the other one should have gone]
He 'got mixed up in' a plan to destroy the government. [=he became involved in a plan to destroy the government]
(..) All right, I got to shower. You guys, um, make yourselves comfortable. Okay. See? People get it. By Odin's beard, this is good Chex mix. No, thanks. Peanuts. I can't afford to swell up in these tights. I'm confused. If there's no costume parade, what are we doing here? (..)2007 TvShow: The Big Bang Theory Title: The Middle Earth Paradigm Season: 1 Episode 6