I don't like my boyfriend's son

I know this is really mean, but it's true. I love the kid, I really do, but I think he's childish and has been babied by his mother way too much. He does things like kick and spit at his sister (also not my child) when he's being naughty and wails and sulks when he gets told off for it. He'll fussily pick and choose which foods he doesn't like this week so that when we have him half of what I cook gets wasted when he loved it last week. And he gets into damn near everything and always grabs my stuff to play with and claim for his own despite being told to ask first. I just find it incredibly hard to bond with him due to all of this.