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).