Cringing looks like this:

If a man proposes to a woman (asks her to marry him) in a public location like a football game or a shopping center, and she says no to him (rejects him), everyone around them will cringe very hard.

More commonly used in a way slightly different from the formal definitions given by Dan.

If somebody does something that is “cringeworthy “, it makes me feel awkward because the behavior I’m seeing is so bad or insensitive. The person doing the behavior doesn’t feel shame.

The character of Michael Scott on “The Office” is famous for some of the most cringeworthy scenes to ever appear on television.

I cringed at the wedding reception when the bride’s father made a drunken toast including several offensive jokes about the groom’s race.

When I watch this video of one of my childhood Christmases, I cringe at how greedy and spoiled I was when opening my presents.

I saw some American tourists in Paris whose behavior made me cringe. They made no effort to speak French and complained loudly when the shopkeeper couldn’t speak English.

P.S. If I do something clumsy or embarrassing, <em>I</em> don't cringe. I make <em>other</em> people cringe.

To "cringe" is literally an action. It is a kind of gesture. It involves face and body language. I know it when I see it. It is the behavior, for example, of someone who expects to be hit, or yelled at. Rather than trying to describe it myself, let me look up a definition in a dictionary, because that is what dictionaries are good for.

1. To shrink back, as in fear; cower.

2. To behave in a servile way; fawn.

For definition #1, imagine someone with an expression of fear on their face. Imagine them stepping backward half a step. Imagine them folding their body a bit to make them look shorter. Imagine them holding up their two arms as if trying to stop someone from hitting them. That's cringing.

For definition #2, imagine someone who likes to be near a bully. Imagine an expression that is a mixture of fear and worship. They keep their body folded a little bit to look short. Imagine that they agree with everything the bully says.

Cringing person: "Isn't it a lovely day?"

Bully: "No, it's a bad day."

Cringing person: "Oh, yes, of course, a bad day, a very bad day, I meant to say bad day."

I know a little Spanish, I don't know Portuguese. Google Translate is showing me the translation "vergonhoso," but, I agree, that seems wrong. "Cringing" is more like fear than shame. It is also showing me two other translations:

Suppose someone does something poorly or clumsily. Someone else says "That makes me cringe," or "that's cringeworthy." This is a kind of exaggeration. It means "it's so bad, that it hurts me to watch it. It makes me cringe: stop, stop, please stop!"

Thank you very much @Joe!