A new one on me
Definition 1 of 1
Pro Tip 1/3Colloquial Usage
Used in casual conversation, often among friends or peers; not in formal settings. 
He rides a unicycle to work? That's a new one on me!
Pro Tip 2/3Expressing Surprise
Indicates that the speaker is surprised or taken aback by new information. 
A cat café in our town? That's a new one on me!
Pro Tip 3/3Not Literal
It’s a figure of speech, meaning the speaker has never heard such a thing; not about physical newness. 
They're making edible balloons now? That's a new one on me.