Currently in IB Spanish. Well in Spanish the word Happy translates to Feliz and the word Birthday translates to cumpleaÃ±os. So the correct way to say it is Feliz Cumpleanos. However unlike in the United States, Spanish culture differs by region and most people just congratulate the person by saying something like Felicidades.
The formal meaning of flex is to show off your muscles, and the slang meaning broadens that to just showing off in general, usually with money. Hip hop duo Rae Sremmurd condemned the activity of flexing in No Flex Zone, and once Nicki Minaj jumped on the remix, it was brought into the mainstream.
SlangSlang is vocabulary that is used between people who belong to the same social group and who know each other well. Slang is very informal language. It can offend people if it is used about other people or outside a group of people who know each other well. We usually use slang in speaking rather than writing. Slang normally refers to particular words and meanings but can include longer expressions and idioms.