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2.
To fight and possibly win a fight against you
you carry on like that, and I'll fill you in
by npeckt September 23, 2009
 
1.
Informal To provide with information that is essential or newly acquired. This is the correct definition of the phrase "Fill You In".
Life's going well (getting better) and I want to fill you in on the details.
by ChrstnSl March 15, 2013