1. One should not say "Modim" in his Shemoneh Esreh twice in a row.
2. One should not say, "And on a bird's nest Your mercy reaches."
3. One should not say, "And on the good shall Your name be mentioned."
4. One should not scoff at anything other than idol worship.
5. One may tell an idolater to put his idol in an uncomely bodily orifice.
A BIT MORE
1. This is because it appears as if he is praying to multiple gods.
2. This refers to the Mitzvah of sending away the mother bird before taking its young (or its eggs). One opinion is that this should not be said because it makes the laws of the Torah into laws of mercy. The laws of the Torah are decrees which must be followed whether or not they seem merciful.
3. This is because we must bless Hashem when bad things happen ("Baruch Dayan ha'Emes") just as we bless Him when good things happen.
4. We find that even the prophets used denigrating terms for idols.
5. This is because one is permitted to denigrate idolatry (when good will come out of doing so).