Equivalent to the phrase "I'm up for it," but abbreviated. It's similar to saying "I'm down." Meaning you're interested in joining in on the activity suggested in conversation.
Ron: I'm really in the mood to get ice cream.
Fred: I'm up.
by JewForensicsGirl February 19, 2011
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Synonymous with "I'm awake." A two word phrase meaning that the speaker is, in fact, not asleep.
Someone getting woken up by their mom: "Ok ok mom I'm up."
by GGGavin June 4, 2020
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Awake; stimulated; conscious and responsive to external stimuli.

1. Some reference texts claim that “I'm up” is defined as physically out of bed. This is too specific to be precise. “Im up” (a colloquial shortening of “I'm up for it”) can also mean “Im down with it”. As spacial references, these definitions cannot coexist. Readers who deal with this inconsistency by choosing one definition and politicking for the exclusion of the other are invited to review the urban dictionary entry for “fuck off”.

2. For phrases meaning on one's feet, see: "up and about" or "up and at 'em".
You up?
(in bed, texting): I'm up.
by FlashPointBang September 13, 2020
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A phrase used to signify to an individual that you are aware of their current level shenanigans and believe that you have surpassed them in your level of shenanigans.

The phrase is best delivered in a condescending vocal tone.
Garfield: Hey! Odie!
Odie: Whats up Garfield?
Garfield: I'm up to you.
by technocrat September 4, 2011
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When your wife, kids, or boss are arguing with you and you want to end it. Signaling the conversation is DEFINITELY OVER.
Used frequently by news anchors.
Wife: Baby, you know that trip I was talking about and the car I wanted, and the dinner party you said you would go to?

Husband: Sorry hon, I'm up against a hard break.
by spudsNbuds February 2, 2011
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The term used if someone likes or does things that are typically found messed up or extremely gross.
I laugh at dead people and people say that I'm fucked up
by Mr.Mistaken March 6, 2018
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A term used to describe that someone is sick and tired of anyone's shit.
Guy 1: JOE MAMA IS SO FAT, UGLY, AND STUPID!!!!! HAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHAHA!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Guy 2: OH MY GOD! I'M FED UP WITH YOU AND YOUR SHIT!!!!!!!!!!!!
by Karma will get you! March 24, 2022
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