nervous or suspicious; acting suspiciously
The teenagers were acting hinky.
alteration of hincty
"conceited," by 1924 in U.S. black slang. Cf. obsolete Scottish hichty (c.1500), considered an alteration of height-y.
Suspicious; curious: Something hinky is going down/ driver of the pimpmobile looks hinky
[1970s+; origin unknown]