Where is their mother? Why do you have to deal with them?

It isn't about the cupcake even, it is about the lack of consideration for others. Why does SD16 get 3 so someone else only gets 1? She should consider that she's not the only one who exists.

My skids do this as well. fakemommy is right through it's the lack of consideration of others. I also think that it's because of lack of structure and boundaries because the parents didn't teach them.

She is HIS daughter. HE should be outraged that she would be inconsiderate of your time and money, and of her sisters' feelings and belongings (since those last 2 cupcakes were theirs).

My response to DH would be:

"I'm upset with you, and I should not have told you that I was just venting. I'm upset that I know you saw my message and instead of being a father and addressing one of your kids taking from their siblings, you left me to deal with it alone. I am taking care of YOUR girls while you are away, but I expect you to still parent when they are being obtuse. No, SD doesn't need to be grounded, but she does need her FATHER to explain why that was rude to both her sisters AND me.

That is why I am upset, because you wanted my permission to ignore your daughter being disrespectful to me and our daughters. The cupcake is a symptom of your lack of parenting causes your girls to think that they not only don't have to listen to me, but that yok silently support it. You shouldn't need to ask my permission to realize that she was being disrespectful. As a parent, it should upset you that your child willfully did not listen to your wife and upset her baby sisters in the process."

I agree with the other posters.  The lack of consideration is the part that kills me and like ITB2012 it is a pattern of this and the non-parenting from DH that makes it more infuriating.  I actually quit going to the grocery before my SD comes for a visit.  Anytime I stock up on things and she has a visit she will devour every snack or sweet that is meant for the whole family.  She will even hide the empty bags in her closet.  This to me is a big issue that DH just doesn't seem to acknowledge or doesn't want to upset fragile SD with.  It drives me crazy.  

I would really love to hide some laxative chocolates that don't say laxative on them and let her devour all those some weekend.  She is the only one that sneaks food and doesn't ask for snacks.  Not that I require the kids to ask me for snacks but mine just usually do and they live there full time.  I hate the entitlement and lack of consideration that SD has when it comes to most everything.  When my YDS has candy (he is 5) she will manipulate him into sharing/giving her some by fake crying and acting upset.  It is really sickening.

If for some reason that I cannot possibly imagine I had to be stuck with a f***tard like your SD I would insist on having control over her phone.   Act like an $$? Well your phone immediately goes into lock mode. 

Maybe you should buy things for yourselves and DDs and let the skids fend for themselves as far as treats go.  It is a mini cupcake so who cares but it's the entitlement that she is more special than anyone.  The only thing worse than an entitled child who thinks they deserve a little extra than everyone else is an adult who behaves in the same way.  Usually adults like that cant hold a job or relationships or friendships.  They are just unlikable people.  My skids are very unlikable and very few people like them besides daddddeeee and a few relatives.  Even their mom barely tolerates them.  She won't take them more than 4 days a month most likely because her husband doesn't like them.