How do you deal with someone who is never happy with their lot...

I find something else to do...

Leave them to it.

Stop listening. They can either try to be positive and make the best of a situation or continue to be unhappy. It's their choice, it's your choice whether you encourage the latter option

Avoid them anyway I can

i live with one of those, you just offer them positivity and if they don't take it then you get on with your day.

You can try to cheer them up. Maybe there's a reason why they moan. Maybe they should broaden their horizons. Geographically and intellectually speaking.

You dont

Ignore and avoid them.

Probably not invite them to watch a good film with me😊

i say there are people out there much worse off than you so shut the f ck up