boastfully usurp
僣 centers on arrogantly overstepping one's bounds: boastfully usurping authority or privileges that do not rightfully belong to one.
僣 is a variant form of 僭. It combines the person radical 亻 with 替, which likely contributes a phonetic element. The exact historical development of this variant is uncertain.
A person 亻 standing beside 替, as if one person is trying to replace another by boastfully usurping their position.
For シン, imagine a boastful usurper putting on a grand show, but everyone sees through the thin disguise: thin -> シン, and the person's arrogance is as flimsy as the act.
usurpation