Not be born yesterday
Definition 1 of 1
Pro Tip 1/3Informal Expression
Used in casual conversation, might not be suitable in very formal or professional settings. 
You can't fool me with that excuse; I wasn't born yesterday.
Pro Tip 2/3Sarcasm Potential
Often spoken with a sarcastic tone to emphasize the speaker's skepticism. 
He said he's never played before and then won the game – sure, I wasn't born yesterday!
Pro Tip 3/3Asserting Intelligence
Implies the speaker is experienced and cannot be easily tricked or taken advantage of. 
I wasn't born yesterday; I recognize a scam when I see one.