I feel obligated to bring a different view after the myriad of hate review embarked on this establishment [not negating your opinions - that's what you experienced] but these are the truth's to mine.
Twelve 1222 Carson is a completely remodeled and revamp bar which replaced the notorious Rumshakers, something I was happy to see as Rumshakers scared into treating it's front entrance like a trained dog with an invisible fence [do not cross]. You enter the bar with a typical layout. To the left a full style bar to the right a dancefloor and a DJ booth with has rotating local DJs each week. To the back there are a few individual taller tables and eat the limited menu. I cannot comment on that as I've never eaten there. [I meant to as they offered $2 taco deals for the mustache march but didn't get around to it]
Now there will be completely different experiences with this bar depending on time and day.
Friday and Saturday nights during prime time:
The bar is located at the end of Carson directly across the street from Jacks, logically when you end up here many patrons will have already had a full night and are exhibit varying levels of behaviors. After 9pm there is a doorman who will scan for capacity and dress code [yes people of pittsburgh - dress code]. Now when I am normally dressed, the wait time is short or I'm treated like one of those obnoxious people who skip lines [life is too short to wait in lines] but I have also gotten turned away for wearing a tank top and raggedy jeans after a hula themed day party and volunteering outside [different occasions] no matter if I knew the management or not. So if you are not wearing a college uniform, you should be fine. As to the rudeness? I just apologize for your experience.
Other Days and Times of Day:
Best day to go is a Sunday night. The bar lays out a free buffet of some appetizers and has a spinning DJ who has played all throughout the hitlists of the past 3 decades. The bar is perfectly balanced, not too packed but there are definitely people out. Also the demographic is slightly older so I say i'm happy not to be surrounded by 21 year olds. During the Day time the Bartender we had saturday was engaging and helpful in recommendations, I was pretty happy to try a Mango Jalapeno Vodka [very good I must say]. No worries about lines and plenty of space to have fun.
My take-away from this Bar. This is a end of Carson Southside Bar so be aware of your surroundings and realize that's what you're going to get. There is a definitely prep-[almost tool] vibe that comes with it so there's definitely room for a change in scenery. However, all in all quite normal, the price point is regular yet pricier in relation to other Southside bars and there is a decent dancefloor. The total location and the bathrooms are clean so good for me.