This is an animated gif of Neil deGrasse Tyson pulling off a great reaction face. During an interview about Sir Isaac Newton, Tyson pulled off this facial expression to show how incomprehensible it is to imagine Newton discovering so many ground-breaking things before the age of 26. He never actually said "Watch out, we've got a badass over here." However, that didn't stop one rage-comic maker from using a cartoon version of this expression with the text "Watch out, we've got a bad ass over here!" written over it.
Neil deGrasse Tyson is a popular American astrophysicist and a science communicator.