The phrase "grease ball" is a slang term used to describe someone who is either very greasy or oily, or it can also refer to a person who is dishonest or morally questionable. Full definition
The oil is lightweight and doesn't make me feel like a giant grease ball when using it. (fcnextdoor.com)
I have used other oils in the past and have looked like a major grease ball. (sweetteaandhydrangeas.org)
He's being a right slimy little grease ball, stick him with the U19s and let him rot, whilst watching the likes of Lacazette, Ozil and other earning up to double what he's on. (justarsenal.com)