CHARLIE SHEEN knows the enabling cycle intimately.  But after so many years as the enablee, it's good to see him stepping into the role of enabler.  That's the circle of life.  Apparently, Charlie just gave LINDSAY LOHAN a check for $100,000 to pay off part of her IRS tax debt.  It's not clear if it's a loan or a present.  But what IS clear is that he sent it, she cashed it, and it went straight to the IRS.

Charlie and Lindsay became friends while they were filming cameos for "Scary Movie 5" in September.  (The movie is set to come out in April.)

Lindsay owes the government $233,904 in unpaid taxes from 2009 and 2010, so Charlie just knocked out about half of that debt.  Lindsay is set to make $2 MILLION this year so she SHOULD be able to pay off the rest, but who knows.