Dad is Coming Home Tomorrow

Assalamualaikum wbt and peace be upon you,

My dad is going to land at KLIA tomorrow morning. I've asked mom if I can follow her to pick up dad, and she said yes. However, my lil sis told her that I said bad things about someone in the school van today, and my mom was very very mad at me.
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Well, it's not my fault coz I'm a talker.Sometimes it's hard to live in Malaysia coz we have to take care of other people's feelings first before we take care of ours. My mom said, "the person's mom might become furious and end up not talking to her."
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In our society, we are not allowed to talk about our thoughts loudly. My mom said" Just say nice things or don't say anything at all".
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But, I'm just not like that. I like to express my feelings and my thoughts. Now, I'm not allowed to follow her to the airport tomorrow. This is all my lil sis's fault. She likes to tell tale. She can never keep a secret.
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How do I keep my mouth shut?
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"Sad"
Daniel Zaydi