What it means
A quick little stamp of respect you throw on someone when they said the honest thing or moved in a way that felt true to them. If you tell someone that's real or so real, you're basically saying yep, I feel that, no fake sauce, just straight human truth.
Usage examples
"You left the party when you were tired? So real for that."
"She said what everyone was thinking, and honestly, real."
"You took one bite, said this isn't worth the calories, and dipped. Real."
"He wore the same comfy hoodie to the function instead of pretending to be somebody else. So real for that."
Where it comes from
From real, genuine and true, narrowed into a supportive way of praising someone for being honest and unapologetically themselves.