Kid Rock says he's VERY sorry for lighting up a fat stogie at a non-smoking venue during a Travis Tritt show in Detroit on Friday ... saying he was way too hammered to know better.

Rock was in the audience at the Andiamo Celebrity Showroom in Warren, MI -- when he fired up a cigar about 15 minutes into the show.

It's not only against the law to smoke at bars in MI -- but it REALLY pissed off a 58-year-old asthmatic man who was in the audience. The man says he plans to file a report with the health dept.

Rock says he feels really bad about the situation ... saying, "My most sincere apologies to the patrons I may have offended, and a big middle finger in advance to all the haters and attorneys who will somehow try to find an easy paycheck in all this."

Rock says he had been drinking pretty heavily at the time -- and explains, "I doubt I'm the first one to ever make a bad decision while being intoxicated."

And he won't be the last.