Is this kdrama inspired by fight club?

Nope. Fight Club didn't invent "protagonist with multiple personalities" trope. So unless Bad and Crazy has anti-capitalism message with protagonist wanting to destroy the economy like Mr. Robot, then no it's not inspired by Fight Club at all

For me it looks like it's a bit inspired, especially when you whink about the scene when ML fights with other men in the basement in ep1

 Mila_no_dramalist:

Agreed with sarepska. It's not an adaptation certainly not a remake, but I'd say it is partially inspired by Fight Club. Even thematically, you could make an argument that while the message is not the same, they have in common to have a protagonist trying to fit in a corrupt world, that gets brutally awoken and made to fight against that world by another part of himself taking the form of a separate personality. Again: not an adaptation, but it would not be crazy to think the writer saw Fight Club (which is after all quite a popular and famous movie) and got an idea from that, then went their own way about it :)

for me they even made some references like K's outfit and the fight ring in the first episode

No..

I Think the therapist is the old friend and the serial killer.. how is the Russian drug mafia tied to the plot idk.. but therapist is involved with the drug mafia as well..

Yes, very obviously inspired by Fight Club, not only in terms of the 'twist' but very overtly, given the way the programme makers acknowledge their inspiration at the very beginning of the 1st episode.

 Mila_no_dramalist:

People know what an homage is, and "homage" and "inspiration" are not mutually exclusive :) You can pay homage to something you were inspired by, and you can be inspired by thing A to make thing B, without thing B being a remake or even that close to thing A.  

There's also really no need to be smug. You can express opinions, and educate people if you think they might be missing something, with kindness. It is, in fact, a really cool way to have them actually listen to what you're saying, and maybe even learn something from you, instead of poisoning the well from the start. 

what on earth hurt your feelings? I never put any emotion what so ever behind the words that I wrote @mila_no_dramalist.. I literally wrote my opinion down. and nothing more. if you took offence by it. seriously that's not my problem, since I never intended anything other than my opinion. whatever you interprited it as, is not on me. 

and I didn't have any emotion what so ever in my words. I wrote them honest and matter of opinion. it was never a matter of feelings, none involved, I wasn't trying to be kind or mean, and there was zero intention of either.. if you use your own experience to look at my words as being agressive and offensive when I just expressed my own opinion without any emotional weight to it. then that is actually not a "me" problem, nor is it in any way an attitude adjustment, I didn't even use an attitude. 

stop being so triggered. it's just an opinion. you obviously have a right to disagree. but take none of it personal. when I say "You all" I literallt mean all humans on the planet or none of them at the same time. I'm neither specific, nor indirect. 

I am legit "just saying" ... 

I can't be held responsible for what YOU feel about ny opinion. if you choose to take offence. that's on you. not me. if you feel targetted, thay's on You and your previous experiences in life. not me. 

what poison in the well? it's only poison if you believe it to be... If my words trigger you, that really sounds like a You-problem. 

quelle que soit votre impression de mon commentaire, de mon point de vue, ce n'était pas le cas. convenir d'être en désaccord.