Chief Keef -- Being Lazy Cost Me $230,000

How NOT to Handle a Lawsuit 101: a lesson brought to you by Chief Keef.

The 17-year-old rapper was sued by a concert promotion company called Team Major back in March ... which claimed Keef screwed 'em over by bailing on a London gig -- set to go down Dec. 29th 2012.

TM claimed Keef's stunt cost them OVER $75,000, including his advance.

Now the lesson part: according to docs, Chief NEVER bothered to respond to TM's suit. After FOUR months of radio silence a judge ruled in favor of Team Major ... simply by default.

Then the judge stuck it to Keef ... ordering him to cough up $230,019 for damages, loss of earnings, and reputational harm.