Basically, I was in a bit of an argument with someone on Facebook, and they called me "ronseal". Kind of as if they were using it as an adjective. I have no idea what this word means. I know it is a brand of wood stain, but that doesn't make any sense. Why would anyone call anyone a brand of wood stain?
IIN that I was called "ronseal"? Can anyone tell me what the word actually means?
IIN that I was called "ronseal"? Can anyone tell me what the word actually means?

First time around it meant someone with too much fake tan (Ronseal are known for making wood dyes).
Second time around (and a better usage, in my opinion) it's used to denote someone who makes an obvious point. A point like, "men have bigger shoes than women because men have bigger feet". The reason for this is because Ronseal's slogan for the past twenty years has been "does exactly what it says on the tin" meaning simple, straightforward, and guileless.
Unless you are orange, I'm guessing you were being accused of making an obvious point.
Try UrbanDictionary. If it really means something, then it'll be on there.