Rex Ryan & Rob Ryan Off the Hook In Margaritaville Fight

When it comes to assault charges in the Rex and Rob Ryan Margaritaville incident -- the situation can best be summed up this way ...

Some people say that there's a Ryyyyyan to blame ... but cops say (doo doo doo doo do) ... it's not their fault. (doo doo doo doo do).

As we previously reported, the NFL coaches were involved in a dust-up at a Margaritaville restaurant in Nashville back in June -- where they allegedly assaulted a fellow patron who wouldn't leave their table.

The man filed a police report for simple assault and officials opened up an investigation into the Ryans.

But now, Nashville police spokesperson Noelle Yazdani tells TMZ Sports ... the district attorney has declined to move forward with charges ... so the case is closed and the Ryans won't be prosecuted.

Bet they'll drink to that!