"What's the capital of Texas?" said the brown hair.
"T," said the blonde.
"What's the capital of Texas?" said the brown hair.
"T," said the blonde.
Alright, listen up, dummy! The joke is that the blonde is soooooo stupid she thinks the capital of Texas is the letter "T". It's funny because blondes are often stereotyped as being dumb. Also, you probably think the capital of Texas is a letter too, don't you?