(slang) A person regarded as foolish or contemptible.
A graduated rod for measuring the depth or amount of liquid in a container, as of oil in a crankcase.
A graduated metal rod for measuring the depth of a substance in its container, as of oil in a crankcase.
(slang, UK) A person of inferior intellect or, more accurately, someone who makes an action that would imply this.
That referee is a right dipstick.