It's a phrase one says when they aren't really kidding but instead use this to take off some of the "truth hurts" pain. While people are laughing because you said sike, you throw in..."But forreal though.."
Jim: Dude your girlfriend is pretty ugly Mike: What ?
Jim: Sike, naw...but forreal though...she's pretty ugly
12 step recovery jargon referring to someone new who talks about how great life is, now that they'resober. Usually meaning that the person is out of touch with reality.
The new guy seems pretty happy for a dude who has no job, no money and no family. He must be on a pink cloud.