Rudeness to fellow commenters is also frowned upon, and usually rejected. We also reject comments for being off-topic, incoherent, unsubstantial and spam, and for using obscenities.
If a comment is respectful, on-topic and avoids YELLING, then it will most likely be approved. One more thing to ensure approval: When you make an argument, defend it. Simple declarative statements like “Obama/Romney is so dumb!” will be rejected. “Obama/Romney is so dumb because of X, Y and Z” will be approved.”