How do you mask your tone?

I feel like i already learned to what to say in situations, and i also know when people are being disingeious most of the time

But the main thing is my tone gives me away and people immedietly consider me a weirdo just by speaking.

Like i had people give me a weird look and a chuckle when i simply said hello to the cashier when i was the one served.

And they repeat back the word i say while doing that rude laugh when someone looks down on you.

It doesn't happen often but even when they dont laugh i can see they looking at me weirdly.

How do you guys deal with that?