This black t-shirt shows one of those famous things that seems to keep happening at The Big Bang Theory.
If Sheldon needs Penny then he will knock her door 3 times and then says “Penny” so on this t-shirt you can see that “knock knock knock Penny!” 3 times and below that the logo of the show but there is more.
Besides the stack of text there is actually a picture of Penny and that makes this Big Bang t-shirt so much better then all the others out there.
If you are looking for a knock knock t-shirt then why not go for this Big Bang Theory Knock Knock Knock Penny T-Shirt.