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.

Person 2: Ha. ICWYDT.

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Person 1: Dude, can you go into your parents room?

Person 2: Uhhh... yeah, why?

Person 1: Because I need you to get my pants back from your mom.

Person 2: ... ICWYDT
by APPLESANDF*CKINGBANANAS January 20, 2011
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text messege/IM lingo for "i see why you do that..."
melissa, understanding cory's jealously in a comment, replied saying, "icwydt cory, icwydt."
by stephanieleann September 28, 2009
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