A lisp
A lisp is when you say 's' and 'z' like they're 'th' and people think you're a stupid kid.
He said 'silly' and it came out 'thilly' and his teacher laughed at him.
She said 'soda' and it came out 'thoda' and I called her a moron.
He tried to say 'snake' and it came out 'thnake' and the dog ran away.