Marcedes Lewis -- NFL Dating Rule ... Steer Clear of Cheerleaders!

They say you're not supposed to dip your pen in the company ink ... and Jacksonville Jaguars star Marcedes Lewis says the same rule applies to NFL players -- don't date cheerleaders!!!

Lewis was out at Boa Steakhouse in L.A. a few days ago when we asked if there are any special rules about cavorting with the ladies from the cheer squad.

That's when Lewis broke it down for us -- "That's not cool ... it's all bad news."

"You just don't do that," Lewis explained ... "especially not your own cheerleaders."

In related news, here's a video of the Jags cheerleaders on a lingerie photo shoot ...