Need advice on how to maturely deal with bratty kids.?

So I'm staying at my grandmother's house for the next few weeks, and my aunt (and her annoying son) frequently visit here. This is my first time meeting the kid, he's three and painfully annoying. He's only been here for the past half hour or so and I'm already about to rip the little s**t a new one. He's constantly whining and nagging for something, every time his mom leaves the room for a split second he's whining and begging asking where she is. I can understand the special bond he has with her, but seriously? I don't want to have to console him every time my aunt has to drop a deuce. I'm usually pretty good with kids and get along with them relatively well but this one is getting on my ast nerve! And he hasn't even been here that long! And he's EXTREMELY rude, he's been insulting my dad calling him a "stinkyhead" and said it in the most not-cute way, and blows him off every time he asks him a question I don't expect him to behave like a cotillion graduate but come on and outright said he didn't like me when i smiled at him and asked him for a handshake at our first encounter...the kid doen't need to be such an ***. He's really loud and annoying and has the most rigid high pitched voice, every time he utters a word I wanna smack the brat in the face. Okay, maybe I'm being a little harsh, and I'm sane enough to not act on anything, but I don't know how to deal with this kid without losing my mind. Dinner's in about 20 minutes, and I wouldn't be surprised if the brat throws his food all over. Any advice on how to stay composed? I'm under the impression that this evening won't be the only time I'll be feeling this during the trip.