Bad Jeff! Bad Bad Jeff! 
Any credibility you might have thought you ever had has been totally shredded.
Bad Jeff! Bad Bad Jeff!
Shredded? That doesn't sound like Jeff. He never uses understatement. Don't you mean my credibility has been "bomb blasted!" ?
Yes, that sounds more like you. It captures the essence of your response without being overbearing. But something is missing. I know, it's not extreme enough. (or overbearing)
"Your credibility has been "Atom Bombed." Yes, that's much better. But wait!
"Your credibility has been "HYDROGEN BOMBED!" Still too weak for Jeff. How about this?
"Your Credibility has been destroyed to the degree that would occur if two planets slammed together." No, that just sounds intellectual and pompous. The intellectual part has got to go.
"Your credibility has "SUPER NOVAED!" No, still not extreme enough. I know.
"Your credibility has exploded upon us like the light of the big bang!"
Let there be light!