In most cases the meaning of the original thought when rendered as a thwat is compromised.
As with a meme (an idea denuded of meaning) a thwat might be thought of as thought without the thinking.
Generally a word subtly replaced with "what" when someone you don't like says something to you from a distance or you can't understand what they said.
You can call them a twat without them knowing and silently giggle to yourself.
"Hey John! GET BUSY OR PRETEND LIKE YOU ARE!"
John replies like he didn't hear him
"I cunt hear you"