How to have "Do not mess with me" attitude.

I am a pushover kind of person, some one who can't convince others and is easily maneuvered. Not that I hate myself but would love myself more if I earn respect from others.

Also I don't make friends easily. Even sitting amongst a group of people I feel lonely, nobody interested in talking to me, to worse it all no one interested in even listening to what I say.

I am invisible, treated like outcast ! :( :(

To cut the long story short I can't and don't wanna take sh*t from others. I want people to think twice, thrice ... before messing with me.
How to have "Do not mess with me" attitude.
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