Grunge hair is the hairstyle of someone who is into grunge music (such as Nirvana, Pearl Jam and Soungarden) and is a proper grunger. Their hairstyle will be long and straggly, perhaps covering a large part of their face.
Tarquin: Wow, you're hair's so messy and cool!
Pablo: Oh, thanks mate.
Tarquin: You must be a grunger with that grunge hair.
Pablo: Yeh, I'm so into grunge. Might as well have the grunge hair too.
Tarquin: Let's go and make fun of some emos!
hair that is usually long, messy and greasy, for guys it isn't layered and might be parted down the middle, grunge hair for girls varies but it might be long with choppy layers or if its short it might be a pixie cut