A person, mainly females, who sucks a lot of dick and gets cumm all over their face. This happenshappens to them them a lot making them "rusted", therefore bringing the name rusted cum-bucket.
David: "Damn I heard that girl over there has been jizzed on hella times."
Ludin: "I know shes a real rusted cum-bucket!"
As per Know Your Meme, the expressionoriginated from 4chan in late 2010, and is used by trolls to "convey feelings of discontent or discomfort in response to someone else’s post in imageboards and discussion forums".
The expression is an alternate form of "u mad bro?".