"Sean Penn's really the only one stupid enough to put anything down on paper"

In this quote, Trey Parker is making an ironical remark about Sean Penn's intelligence. He is indicating that Penn is not really wise since he is the only one who would write something down on paper. This might be analyzed as a jab at Penn's composing abilities or his decision-making abilities. Parker is suggesting that composing something down on paper is an absurd or unneeded action, and Penn is the only one who would do it. This quote could also be viewed as a playful dig at Penn's credibility as a serious and intellectual actor. Overall, Parker is utilizing humor to satirize Penn's perceived intelligence.