plaster hair down
plaster (one's) hair down
To cause one's hair to lie flat on one's head by using a large or excessive amount of water or hair products (such as oil, cream, gel, etc.). I don't understand why you plaster your hair down with gel like that—it looks so geeky! I get such bad bedhead that I have to plaster my hair down with water before I can even run a comb through it.
plaster one's hair down
Fig. to use water, oil, or cream to dress the hair for combing. (The result looks plastered to the head.) Tony used some strange substance to plaster his hair down. He plastered down his hair with something that smells good.