1. interjection Against the run of natural justice. P1: "So I stole your cape - that makes it mine now." P2: "Unfair!"
2. adjective Mistreated by the game. "You changed the way the LS worked and never told anybody! That's unfair!".
3. adjective Subject to (suspiciously) bad luck. "Every time the Z6 moves, I walk right into its room. That's unfair!".
4. adjective Illegal, but performed by an individual who seriously outranks you. "Don't you think that FODding someone for having the same name as your cousin's dog is a little unfair?"
5. adjective Exceeding reasonable bounds of generosity or meanness from a position of power. "You can't give her back her T, that'd be unfair!".
6. adjective Contrary to what the speaker wants.

Continued use of senses 1 to 5 will generally lead to them all being interpreted as sense 6. "I can't open the portcullis on my own. That's unfair!". Yeah, whatever you say...