What is For Seriously?
1.
Used to back up a statement that is strongly true.
Person A: Dude, the performance of Berlioz's "Symphonie Fantastique" was the best thing ever!!
Person B: For seriously!
See
2.
Often used to show excitment with underlining uncertainty.
Person 1: I had a car crash, but no one was hurt
Person 2: For seriously?!!
See