Answer: - Curses and insults

- Saying that someone is an animal or the like

- Saying obscene or indecent words

The Prophet (may Allah's peace and blessings be upon him) forbade all such things by saying: "A believer is neither a slanderer or an invoker of curse, nor is he indecent or foulmouthed." [Narrated by At-Tirmidhi and Ibn Hibbān]