Is London dialect the most prestigious accent in the world?

<I got laughed at by my classmates at school for speaking with a British accent.>>

It's called 'tall-poppy syndrome'.

''I got laughed at by my classmates at school for speaking with a British accent''
Maybe they didn't understand you. Your classmates read Harry Potter translated from British English.

''Is London dialect the most prestigious accent in the world?''
Yes, Cockney dialect is the most prestigious accent in the world.
Not!