He then proceeds to scoop it out and throws it at her face.
This is not dissimilar to the way a monkey throws feces at its fellows.
"Yea man, Billy is the greatest."
"Monkey" can also be used more broadly in the sense of "ape-like creature" or to refer to a person who resembles such a creature, such as a troglodyte. This is generally an insult (rarely, referring to a silly clownish person, it is not as harsh). In any case, the monkey generally enjoys the following:
-stealing things, especially food
-hurling excrement at people (see also politician)
-comic mischief in general
A KKK rally is just a bunch of drunken monkeys.
Look, the monkey is making a speech again on TV! He's not very good with English, but maybe he could learn sign language like that gorilla everybody loved.