google "what is the difference between formal and informal speech?" many hits ... https://www.uts.edu.au/current-students/support/helps/self-help-resources/grammar/formal-and-informal-language [excerpt] What is the difference between formal and informal language? Formal and informal language serve different purposes. The tone, the choice of words and the way the words are put together vary between the two styles. Formal language is less personal than informal language. It is used when writing for professional or academic purposes like university assignments. Formal language does not use colloquialisms, contractions or first person pronouns such as ‘I’ or ‘We’. Informal language is more casual and spontaneous. It is used when communicating with friends or family either in writing or in conversation. It is used when writing personal emails, text messages and in some business correspondence. The tone of informal language is more personal than formal language.

In the UK, we speak informally in pretty much all situations. I imagine (and it's my observation) that it's the same everywhere because informal doesn't mean impolite. Neither does it mean slang. You'd speak formally when delivering a lecture, in a law court, when making a speech, etc. But in most situations, we're formal or semi-formal. In fact, speaking formally can actually be impolite because it can seem very unfriendly.

Diego, regardless of where you're from, you speak informally with friends/family. Rarely will you come across someone who speaks their language exactly like the grammar books prescribe. That's called a vernacular. I see you're from Costa Rica. What do you think of words like "monchar" or "pichúo"?

You’re right, the only people who speak informally are vagabonds and people on the street if you lived in a tube and never saw a saturday morning cartoon, lived in a country or ever been to planet earth. But if you grow up in “the world” chances are you speak informally. This sounds like a troll post to get responses adding the only druggies speak informally at the end. well done sir. Troll level up

We are the kings of bad manners.