The phrase "most pissed-off" is often considered as a colloquial or slang term used to describe a person who is extremely angry or irritated. However, there are several synonyms that can be used to convey the same meaning. Some of these synonyms include "outraged," "enraged," "furious," "incensed," "livid," "infuriated," and "irate." These words are more formal and suitable for use in formal or professional situations where the use of slang is inappropriate. Choosing the right synonym to describe anger or frustration can help to add depth and nuance to a piece of writing or conversation.