Sean Spicer Accused by Former Classmate of Calling Him the N-Word

Sean Spicer's book signing got heated very quickly when a former classmate of his showed up to confront him ... and shouted out a serious n-word accusation in front of Sean's fans.

The former White House Press Secretary was signing copies of his new book 'The Briefing' in Middletown, Rhode Island Friday, when a man named Alex Lombard -- who attended prep school with Spicer -- accused him of trying to fight him when they were teens ... then claimed, "You called me a n***** first!"

The people waiting in line initially laughed at Lombard bringing up his past with Sean, but gasped and groaned at the n-word allegation. Lombard was then led out by security.

The vid by Newport Daily News doesn't catch Sean's reaction to the racial slur accusation.