DIDDY SUES FOR $2.5 MILLION IN DAMAGES!

The storefront of the Sean John store in New York City is quite impressive ... or at least it was, according to a new lawsuit -- and now the company that runs Diddy's clothing line is suing the people who allegedly messed it up. According to a lawsuit filed in New York, Diddy's company -- Christian Casey LLC -- leased a portion of a ground floor building on Fifth Avenue in NYC for its flagship clothing store.

Diddy lawyers claim sometime in 2006 the building owners put up sidewalk scaffolding and just left it there -- sending Sean John sales down the toilet -- down nearly 50%.

They claim the scaffolding "substantially obstructed the view of the clothing and furnishings displayed in the ground floor windows."

Team Diddy is suing for $2.5 mil in damages ... minimum. FYI, that's roughly 12,500 bottles of Cristal -- minimum.