So I'm looking for some manga with really badass mc. Like something with a nonchalant mc that really good in what they do and/or an overpowered mc or the mc gets strong fast?

Some examples that I've really enjoyed are:
-Black Haze
-Bartender
-Shokugeki no soma
-Noblesse
-Murcielago
-Skip beat
-Adekan
-The new gate
-Doulou dalu

Thanks for any input, anything is much appreciated!

Dendrobates maybe? There's also Until Death Do Us Part.

[img]http://www.nodiatis.com/pub/11.jpg[/img]

Golden Kamui and Blade of the Immortal both have the unstoppable kickass type
Historie the ever talented hero uses swordplay, intelligence, creativity, and sheer luck to realistically yet ridiculously overcome obstacles
Giant Killing about a former football prodigy turned brilliant manager bringing the best out of his club
and maybe - but a bit of a stretch - Mushishi with the mysterious yet ever reliable Ginko.

Kaibutsu Oujo Hime, oh so very much...

Hiro gets there eventually, but spends much of the manga mostly as cannon fodder... in the end he is more or less some kind of immortal-firethrowing-superhuman-thing

Jormungand Fits more or less EVERY character in this one... at least the named ones anyways.
Full Metal Panic! Raised as a soldier from childhood... and he's very good at it (but only that as it turns out...)
Denpa Kyoushi OP mc of the genius intelligence kind.
Aiki

He was so OP his father broke his joints to prevent him from getting better at fighting...

Wizardly Tower Ancient wizard wakes up after sleeping for 1000 years only to find that the magic he knows is now the stuff of myths and legends... sort of like The New Gate actually...

~4400 manga completed
~1700 ongoing...

Seconding Dendrobates -- it really fits your description, imo. A manga with a very similar ambience is Jiraishin.

Muhyo to Rouji no Mahouritsu Soudan Jimusho has two male leads, and one of them is like this.

Liar Game -- Technically, the female lead is the protagonist and the nonchalantly cool/smart male lead is the deuteragonist, but otherwise a good fit. Ditto for Ghost Hunt and Shinrei Tantei Yakumo (Novel).

One Outs
Kakegurui
Reinouryoukusha Odagiri Kyouko no Uso
Muteki no Hito
Akagi
Cesare
Drifters
Hellsing
Kino's Journey (Novel)
Gundog
Hotel Tantei Doll
New York no Benkei
Zero - The Man of the Creation
Gallery Fake -- Has an anime (the manga isn't being scanlated).

Sakamoto Desu ga? fits in a technical sense, because the MC excels at everything he tries and is a really good guy besides. However, it is a gag/comedy series, so YMMV.

Vinland Saga? I dropped this years ago, though, so I'm not certain. Same goes for Vagabond.

The Protagonist strong from the start category should have quite a few titles you'd like, too.

Btw -- not all of these characters are OP in the action sense, but since you mentioned Bartender in the examples, I'm assuming you're also open to suggestions of intellectually OP MC's.