When you get ignored by someone here's what you do...Find a red tablecloth and/or large piece of red fabric. Fashion that fabric into a cape. Next find a pair of stirrup leggings. Now grab some glitter, but make sure it's non toxic, you never know. Run around and throw glitter everywhere and sing Journey. You'll get their attention.
In all seriousness (although the above would be a great way to spend a Friday night) I know what you mean and it isn't fun to feel like you're being ignored, whether you are in reality or not. That said, sometimes it's just a matter of human nature when people are absorbed in their situation they forget to include others, which isn't very nice, but it's often not personal. In other cases, some people just have sand in their pantaloons and they're just not nice. Try and focus on being a good, kind person, maybe being more assertive if you really do want to talk to certain people, and take the rude people with a grain of salt and try to move on and not dwell on it.