Welcome, GiveMeAnAspirin!
I am a Catholic.
So am I, again. I was away from the faith for about 35 years, and was the "unbelieving mate" of a JW for about half that time. I returned to the faith after she divorced me.
I've been wondering why active JWs are so anti-catholic; is it part of the teaching they receive in the Watchtower?
Yes, it is part of the teachings. Their anti-Catholic stance (anti-mainstream-religion in general, as Flipper points out) became entrenched under their third president(*), lawyer J. F. Rutherford. He was anti-almost-everything but reserved particular vitriol for Catholicism. He was the one who stopped calling the followers "Bible Students" and introduced the name "Jehovah's Witnesses".
Recommended reading: A Catholic Critique of Jehovah's Witnesses. This details their beliefs, and confirms what most people on this forum say about them.
(*) Most Witnesses think Rutherford was #2, because the Watchtower Society has whitewashed their history to remove mention of William Conley, one of the five founders and the
first president of the religious group now known as Jehovah's Witnesses.