Well, I cannot say for certain in these particular scenarios, since I do not possess enough information to make a judgement, but sarcasm is often intended for humorous purposes (not always). This said, while it may seem accusatory in nature, it is often simply a light-hearted method of picking on someone else -- nothing personal. Of course, this is not always the case, but I find it to be just that more often than not.

Still, some people are downright rude at times, but chances are, in these situations, they are merely projecting their own insecurities elsewhere. It all really depends on the circumstances and the individual.