1. To think so highly of oneself that all others are viewed as being separate.
2. To think you're better than all others and that you are all that matters.
3. High maintenance, uppity.
From the root "sedition" noun, which Merriam-Webster defines as "incitement of resistance to or insurrection against lawful authority"
inciting or causing people to rebel against the authority of a state or monarch : the letter was declared seditious.
ORIGIN late Middle English (in the sense violent strife ): from Old French, or from Latin seditio(n-), from sed- ‘apart’ + itio(n-) ‘going’ (from the verb ire).