All the gang bangers forgetting about the drive-by isn't nearly as bad as Montell Jordan forgetting to pay his taxes ... to the tune of $627,987.06, this according to docs obtained by TMZ.
The "This Is How We Do It" star owes Uncle Sam back taxes for the years 1999-2001. According to the Federal Tax Lien filed against Jordan, the government first filed a lien against him in 2004 -- but since he still hasn't paid up, they refiled it last month.
The IRS is looking for their money ASAP and if they don't get it, they can go after his property in court.
A rep for the singer tells TMZ the government has to get their groove on before they can get paid.
(Just kidding, the rep didn't get back to us)