I can't even!
American SlangDefinition
A hyperbolic expression signaling being so overwhelmed by strong emotion—shock, amusement, frustration, or disbelief—that one is momentarily speechless or unable to cope.
Examples
"The cat knocked over the wedding cake five minutes before the reception, and the baker whispered, 'I can't even!'"
"Watching the toddler nail a perfect dance routine, I doubled over laughing: 'I can't even!'"
"When the bill arrived and it was double what we expected, he stared at it in disbelief and said, 'I can't even!'"