NFL Star's Agent -- You Can't Use the F-Word?

Larry Johnson's agent claims he's appealing the KC Chiefs decision to suspend the running back for dropping a gay slur this week -- but the real story is that the agent claims he "didn't realize" the F-word was offensive in the first place.

TMZ spoke with Peter Schafer -- who is also Johnson's lawyer -- who explained:

"We know the N-word is unacceptable, that's not disputable -- but f*g? I'm learning that there's a segment of our society that finds it offensive and that it should not be used. I didn't realize that, but I do know now..."