What does Tu es petite pen mean?

"Tu es petite pen" is grammatically incorrect French. It should be "Tu es petite, Penn" or "Tu es petite, Pen"

Here's what it means:

* Tu es petite: You are small.

* Penn/Pen: This is a name.

Therefore, "Tu es petite, Penn" or "Tu es petite, Pen" means "You are small, Penn".

It's a statement describing someone named Penn as being small.