She doesn't like to point out her hoof for anything that may get her dirty and yes in fact her behaviour has been threatening, with the obvious example of Look Before You Sleep (she's undoing Applejack's chores, with consequences that were shown later on in the episodes). Whether threatening or not, Rarity is occasionally as vain as one can get.
In The Ticket Master, Rarity is just as greedy for the tickets just as any other, completely ignoring she bears the elemnent of generosity. A beautiful example that some of the main 6 have: if one's element clashes with the plot of an episode, this element just gets ignored. In Sonic Rainboom, she (though unknowingly) steals Rainbow Dash's opportunity to make a good performance. Whether "stealing spotlight" could be considered ungenerous is up for debate, but I think it isn't how she should act. She was, again, vain, to say the least. In Secret Of My Excess she was also obsessed with Spike's birthday gem. Seems like he took over her trait for a minute there when he decided to give it to her.
As I said about her generosity not being genuine, I mean it's often shoehorned in, doing it for the sake of being the element of loyalty. Of course in Friendship Is Magic, this had to be mentioned. In Suited For Success she gives free dresses to her friends but I still think this is good. It's episodes like Rainbow Falls that basically say: "Gee Rarity, you are so kind to give us these dresses. After all, you are the element of GENEROSITY."
I don't think we can know how Rarity could know those Diamond Dogs would be such retarded creatures. There is nothing tricky or cunning about straight-out whining your lungs out. It's what a child would do. She might as well had been punched knock-out if this show wasn't as lighthearted as it is (which is something I enjoy - don't get me wrong). I dearly hope there are any other instances where Rarity is showing her intelligence and she succeeds, can'