A modern adjectival outgrowth the noun "shyster." The original term refers to someone who behaves in a disreputable or unethical fashion. Thus a "sheisty" person or behavior is one which appears overtly, even lewdly, unscrupulous.
The origin of "shyster" may be from the German "Scheißer" meaning pooper (MW) or from the old use of "shy" meaning disreputable (OED).
The guys at that party were completely sheisty.
You look really sheisty when you grease your chest.
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