Bangs

SUMMER: You should get bangs.
PARIS: Thanks for the tip.
SUMMER: You have a long forehead. Bangs would hide that.

Bangs is another word for a fringe, hair cut and styled so that it falls over the forehead. Apart from her classic “mean girl” put-down in the guise of being helpful, Summer may be making a play on the word “bang” for sex, so that she’s telling Paris, “You should get banged”, so that she will chill out and stop getting jealous.