Devilishly Rotten
I'll be frank in saying most of the time, I think it looks trashy and I don't like it.
I know that it depends on the quality of the job, the person wearing it, blah blah blah, and sure, I've seen exceptions to my general opinion where I go "holy s**t, that hair's gorgeous", but it's not even close to often enough to make a difference in my thoughts of unnaturally dyed hair as a whole.
I agree, most of the people I see with unnaturally colored hair look pretty trashy.
If you want to dye your hair an unnatural color,
get professional help.
That way, they apply it correctly and you have a less chance of messing up. They can also tell you if that color is going to actually look good on you. I have seen so many girls with fire engine red hair and it doesn't look right. The same with pink, blue and most pastel shades.
But, as someone who has dyed her hair a billion colors, I can't say I'm against coloring your hair unnatural colors.