Messaging "friends"

Ok so i message this girl on tagged, and what happens, she starts getting mad at me because i sent her a message that said whats up, i mean you are on my friends list, i can assume if you are on my friends list you don't have a problem with me, why do people just add for the sake of having someone who has a lot of friends, i mean do they not think that we will talk to them, we are real people, what is her deal, note to all of you, don't look surprised when one of your "friends" on a social network says hi, just because a lot of ppl out there just add for the sake of adding you might just run into someone that doesn't, get over yourself, if you don't want to talk to someone just take them off your friends list, is that not common sense?