First of all, it's completely okay to be a sensitive person. It's your personality and you like expressing or letting it out verbally or emotionally. Fuck the ones who make fun of you because they can't be half the person you are. I really wouldn't want you to not cry just because someone else makes you feel that way. Trust me they ain't worth it.

That being said, if you still want to make yourself not cry,

1. I used to watch this anime that made me cry a lot over and over again until i stopped crying. Usually it helps me but I can't say the same to others. (I lost emotions due to my occupation but that doesn't mean i don't cry .. i do too and it's really ok to)

2. Practice in the mirror. You need to learn to make a poker face. Slowly and steadily it will come up

3. Identify the things that make you cry. Make a list of it and slowly work on it. If it's someone else that's making you cry... Tell yourself everyday they aren't worth it and fortify your mind. Sooner or later it will kind of work.