to hit up
1a The slangy verb to hit [someone] up for [something] is used lightheartedly in the sense of asking someone for money, a cigarette, a job... something someone has that you want or need.
Aidan's car broke down in the city and his brother came to pick him up after it was towed to the shop.
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Jim: Hey, I got here as fast as I could. I was at the gym when you called.
Aidan: No problem. Thanks for coming.
Jim: So what happened? The car wouldn't start?
Aidan: No, it started, and I made it downtown, but when I left the library, it started smoking like crazy and just stopped.
Jim: Damn. How are you going to get to work tomorrow?
Jimmy: My next door neighbor works in the same building as me. I'll just hit him up for a ride until my car's fixed.
1b This verb is used innocently enough in the (1a), but hit up usually has a bit of a negative connotation; it implies that the asker is desperate or annoying... for instance, an irresponsible friend hitting you up for rent money because he squandered his entire paycheck over the weekend or a boy hitting his dad up for an expensive gaming device, etc.
So when someone says they're going to hit their boss up for a raise, they sound like they're doing so at the risk of being viewed as annoying or inappropriate or even desperate — perhaps they know they don't deserve the raise or they feel the boss is going to turn them down even before they ask, but they decide to try their luck anyway.
Whatever the case, this verb usually carries a nuance of intrepidness and shamelessness on the part of the asker, as well as inconvenience or offence to the askee.
Roommates Robbie and Jack are out and about on a Saturday morning when they spot an old classmate downtown, begging on the street.
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Robbie: Oh my God, isn't that Alan Baxter?
Jack: Yep. He's out here every day. I always see him when I go on my lunch break.
Robbie: What the hell happened to him? He was such a badass in school.
Jack: Well, that's what drugs'll do to you. He's still young and able-bodied, but he's out here with that dog, hitting people up for money for "dog food", but we all know where that money's going.
Robbie: What a nightmare...
2 The phrase to hit [someone] up is used in the sense of calling, texting or otherwise contacting someone — especially if you want to hang out or go out with them.
But it's also used in the general sense of «Call me sometime!» when running into someone you haven't seen in a while; or generally to say goodbye to someone. You'll often see this abbreviated to HMU in chats and texts.
Dean is in London for a conference and runs into an old friend on the street.
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Dean: Well if it isn't my old college roommate!
Ron: Dean! What the hell are you doing here.
[the men embrace]
Dean: Apparently, the same thing you are — business! What's it been, ten years?
Ron: At least!
Dean: Where are you living these days?
Ron: Atlanta. Just moved there last month.
Dean: What?! That's where I live.
Ron: Shut up!
Dean: I swear. Been there five years now. Dude, you have to hit me up when we get back — we have a lot of catching up to do!
Ron: Count on it!