Idby

This has two meanings. It can mean "I don't believe you" or "I don't blame you". Just the same abbreviations.

Max: I just met a celebrity 5 minutes ago!!
Sam: Really? No, bruh... Idby (I don't believe you.)

Or

Max: I'm very worried about my girlfriend. she hasn't texted me in days.

Sam: I would be worried too. Idby (I don't blame you)