Curmudgeon

Grandpa was a real curmudgeon to the very end.

Don't be such a curmudgeon!

How did you become such a curmudgeon? You used to be so cheerful all the time.

If that old curmudgeon had had any children, he might not have become such a curmudgeon in the first place.

Near-synonyms: crank, grump; grumpy pants (often childish), sourpuss, grouch

There's a cranky curmudgeon working at the hospital who gives all the patients and other doctors flak.

John Doe's old age and stubborn aversion to new ideas make him a curmudgeon of a candidate.

After a while, as cultural debates became more polarized, the editorial tone of the New Criterion went from being charmingly curmudgeon to being bitterly shrill.

How to Be a Curmudgeon on the Internet

How should I respond, without appearing to be a curmudgeon?