u/ means username/ and it is used in Reddit and is well known in the Reddit community. People use u/ insert random name here to mention a random Redditor to tell them to get their butts onto a post or to show others who the person is. BE AWARE that when you mention somebody they can see what you commented that made them go onto the post
Anne: Hey Harry how do I mention a Redditor again I'm still new to this website, please help.
Harry: You just type u/ and then their Reddit names and there you go that's the dummy's guide to mentioning somebody on Reddit.
Anne: Did you just call me dumb?!
Harry: No...
Harry: You just type u/ and then their Reddit names and there you go that's the dummy's guide to mentioning somebody on Reddit.
Anne: Did you just call me dumb?!
Harry: No...
by u/welikeReddit1 January 20, 2021
Get the u/mug. Phrase used to counter any insult no matter the intensity. This will reflect any insult back to your enemy with the effectiveness of a 100x
by Third grade niggas May 10, 2018
Get the No Umug. by WOW I LIKE IT February 1, 2021
Get the u smell like bitch poopmug. 
A deflection; basically the modern version of "I know you are, but what am I?"
If you ain’t got an uno reverse card on you.. this right here.. will leave ur opponent SPEECHLESS.
If you ain’t got an uno reverse card on you.. this right here.. will leave ur opponent SPEECHLESS.
Opponent: this is why no one will ever like you. You’re literally such a dumbass istg
Me: No u
Opponent: ...
Me: no u
Me: No u
Opponent: ...
Me: no u
by ayana yktv 🤪 December 30, 2019
Get the No umug. 'No u' is a simple comeback given by simple people. People will use this term when they can't think of a decent comeback fast enough and will usually think that they have won an argument by finishing up with a classic 'no u'. They haven't won the argument. They just made themselves look like a a thick nonce.
by thelittlestofblondes July 30, 2019
Get the No umug. Ayo where u at?
by DozerSpelling September 7, 2022
Get the Umug.