Fat Joe -- I'm Not Thrilled About Prison Sentence

Question: How does Fat Joe feel about going to prison for 4 months?
Answer: He ain't exactly thrilled.

TMZ spoke with Joe moments ago ... and (shocker) he didn't seem too jazzed about yesterday's court hearing, when he was sentenced to 4 months behind bars for stiffing Uncle Sam out of more than $1 million in income taxes.

In fact, the rapper kinda had an "It is what it is" mentality.