Acceptable people to have brunch with:
1) Your girlfriends: For the purpose catching up on everyone's night before over pancakes and eggs benedict. It's a perfect meal to pig out on early enough in the day where you still have time to burn it off.
2) Your new boyfriend's parents: It's less stressful than dinner because there is an allotted amount of time. It's not usually that expensive so you don't have to feel awkward about the parents picking up the check. You can look chic yet still conservative. Perfect parent brunch outfit: skinny jeans, flats, a cardigan and colorful scarf with some cute earrings. Voila.
3) That guy you just started dating and slept over at your place for the first time: Let's be honest, if he wants to go out for brunch after, he likes you. If he has to run out to meet friends/ run a marathon/ watch football he's just not that into you. It's a good barometer.