Nah, but i've heard of it
What your friend says when they’re too proud to say they don’t know what you’re talking about and think they do
'Nah, but I've heard of it' when you told them about a new video game and they had no idea what it was.
'Nah, but I've heard of it' when you asked if they knew what a meme was and they said they did, but they didn’t.
'Nah, but I've heard of it' when you mentioned a new song and they said they’d heard of it, but they hadn’t.