I understand that we use "is" for singular and "are" is for plural. But I've heard so many times, for example: "This is my hands". And I don't remember other phrases where people use "this is" for plural. I mean, I've heard it not on the streets, but on TV (SNL).
I have not come across this is followed by a plural verb and would be interested in any examples that you can provide.
You might hear somebody say This is vegetables and that is salads, meaning that this area is set aside for vegetables and that area for salads. But that construction is merely eliding a word such as area or zone.
On the other hand, it is relatively common is here there is followed by a plural verb, as in There's lots of people waiting to see you.
Without having examples of what you've seen it's very hard to say why that construction was used. It's incorrect when taken literally.
By 'SNL' do you mean Saturday Night Live? If so, please understand that on a comedy show there are subtle, unspoken meanings and references behind almost everything the actors do and say. They are making fun of some person or group or some part of the culture. They might deliberately say things in an unusual or incorrect way to create a comic effect or make fun of somebody. It might be that what you heard really is incorrect English used on purpose for entertainment.