Credit to @Madibear_ for this idea! Hope this helps!!
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1. Ask that sibling why they are doing it. They always have reasons! Usually, if they're younger, it's because they want to spend more time with you. Be sure to ask in, not an upset voice, but a calm, polite voice,and try not to upset your sibling either!
2. If they poke, shove, or shake you (hitting too), just get a parent. Telling a parent is more reliable because if you annoy them back, sometimes they will tell on you for annoying them. Try to be the bigger person and always stay positive with them.
3. Try to be close to your parents and if they ever annoy you, tell your mom and dad! By this time, your sister or brother will get tired of you telling on them so eventually, they will stop.
4. For people who aren't really comfortable with telling their parents, try to inhale, exhale, when you are annoyed. You can try to squeeze those tears out of your eyes, it might make them feel bad and stop. That works a lot. Also, if your sister/brother has a counter for that (acting hurt or something and pretended you did it) try to use reverse psychology. If you feel as if you don't think your parents are going to help you in this one, go try to do something to calm your fears such as reading, exercising, day dreaming,shooting hoops, sleeping, drawing, etc.
5. Tell them to put things into perspective. Chances are there is someone who is dealing with something worse, bring that up to them so they can become a little bit more soft.
6. Tell them they're just getting into trouble! They will not understand, but who cares?
7. If None of the above work, you should just do exactly as your bro/sis does. Keep copying them for about 5 hours. It may sound hard but the result is worth it! If they try something like 'I am stupid' You just turn it around to 'Yes you are'!
8. Go to the parents. Let them deal with it. It's off your hands and into someone else's.
9. Try your hardest to be better friends with your sibling, and get to know them better.
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I know some of these sound stupid, but trust me, they work. I hope these tips helped! Credit to WikiHow for these tips. Don't forget yo leave your suggestions for updates in the comments!