Today I saw an idiomatic road sign: "Pretty Muddy". I found this lack of strict English on a road sign unusual (on par with my "Dead Slow" official speed limit sign in Leeds, pic below), but as it turned out it's a charity race and the signs were merely directions.
This got me thinking however, how do words like "pretty" and "dead" as intensifying adverbs end up in English? Taking "pretty" as an example, when did this first appear?
I wonder how fast you have to be going before they stop you. How would this hold up in court?