Literally speaking, you have nothing else to say and don't know.
Can be used to exit/end a conversation, justify a break-up/cheat-on, and as an excuse for not wanting to think.
This phrase has an angry/indifferent/anxious undertone.
This phrase can also be followed by ", eh eh." often referenced by Monsters from "Eh Eh (Nothing Else I Can Say)" by Lady GaGa.
1. A: "I can't believe you fucking slept with him last night, you promised you'd never cheat on me..."
B: "I was so wasted last night, I'm sorry..."
A: "There's nothing else I can say."
2. A: "Did you seriously max-out my credit card...?"
B: "It was an accident... there's nothing else I can say..."