A person who eats a freakin ungodly amount of your food without caring if anyone else has eaten yet or who eats all of your leftovers leaving your refrigerator completely empty.
to focus on what is more important, it's a variant of getting your act together or getting your priorities straight, it's sometimes used in a hilarious tone or serious tone.
person 1: look, I know this is serious, but you need to get a marker straight on your homework, just trust me about your homework.
person 2: ok, I promise I'm just gonna stop watching BFB and prioritize my homework over BFB.