Let’s see this shirt has a castle and the word silly. Let me guess: Monty Python and the Holy Grail. I’ve seen that movie about 4 times, but I can never remember anything, so I’m not sure if this comes from that fine cinematic experience. Let me go check real quick.
Yes! Knights of the Round Table/Camelot Song.
“On second thought, let’s not go to Camelot, ’tis a silly place.”