Is Derren Brown thick

No, actually.

Derren Brown has a higher IQ than the average person.

Derren is educated in hypnotism, mind control, theatrics, psychology, mathematics, Biology and so on.

Chances are, Derren knows ten times as much as you know.

In fact, your usage of the Word "thick" in your question shows that you are generally uneducated and have a borderline average or even below average intellect, since intelligent people use terms such as "mentally challenged", never the Word "thick". The fact that your original question referred to him as "Darren" instead of "Derren" and lacked proper capitalisation (until I fixed the question) confirms this.

Your usage of the Word "thick" also implies that you are hinting at jealousy towards Derren Brown's intellect or abilities to such an extent that you feel you have to attempt to regard him as "thick" to make yourself feel better about the fact that Derren has and will achieve much more than you. Yes, I used psychology to answer this.