EXCLUSIVE

When you go to the "Today" show with a shirt suggesting Bill Clinton did what Donald Trump said he did ... you gotta be ready for someone to kick your ass ... so says NBC.

Mark Gallagher went to 30 Rock before the election and wore a t-shirt with Clinton's face and the word "rape."

He claims he was standing there minding his own business when NBC security -- whom he called a "goon squad" -- descended on him and beat the crap out of him. He has sued NBC for $53 mil.

NBC has now fired off its answer, saying when someone does something as incendiary as Gallagher did, they assume the risk someone will come after them. NBC does not get specific, but the network disputes Gallagher's version of the facts ... presumably what he did before the incident.