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.
Spicer's book tour has not been going smoothly so far -- he was heckled at another signing in NYC Wednesday and called a "garbage person."