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.
Slang is the use of informal words and expressions that are not considered standard in the speaker's language or dialect but are considered acceptable in certain social settings. Slang expressions may act as euphemisms and may be used as a means of identifying with one's peers.