ICWYDT is also commonly mistaken for ISWYDT (which means 'I see what you did there') because of 'text language' and 'internet slang' using the letter 'C' as the word 'see.'
ICWYDT means "I 'see' what you did there."
'I see what you did there' is commonly used as a sarcastic response, as it is a clever turn of phrase.
Person 1: Ahhh, I remember back in the day... when it was morning.
when you're holding up your phone and making faces at it, as though you are taking a selfie, but you're really taking a picture of the person across from you or the wall or anything else that seems interesting but you don't want to be caught dead taking a picture of.
This action is often made more convincing by wiggling the eyebrows or opening the mouth, to pretend you're trying to get a Snapchat filter to work.
FRIEND A: "Did you just take a stealthie of me?"
FRIEND B (turning phone around): "no I was just using snapchat's new filter, see?"