Come On

1. Come along with me; join me in going.
2. An expression of encouragement.
3. An expression of disbelief.
4. An expression of frustration, exasperation, or impatience; hurry up.
5. An expression of defiance or as a challenge; approach; come at me.

(encouragement): carn, c'mon

(disbelief): come off it, c'mon, get out of here; bullshit