What's the difference?

euphemisms are phrases that are "nicer", for example, "passed away" rather than "died"

idioms are phrases that are just totally different from their real meanings, for example, to "kick the bucket" is an idiom.

Idioms are expressions that mean something to the speakers of the language the language. He's the cat's pajamas. This is an idiom, it means that is a good fella.

A Euphemism is a way of expressing a negative in a positive light: "My hangovers were actually very educational experiences." That's a euphemism because a hangover is actually a head ache and nausia... maybe vomiting and uncontrollable diarrhea.

The difference is the degree of possible offensiveness. An idiom is a phrase understood within a certain culture to mean something other than the words themselves, like "clean your clock" meaning beat you up, or "booking" meaning leaving. A euphemism is a word or words used to describe something that could be offensive, like "a roll in the hay" meaning having sex or "going to see a man about a horse" meaning going to urinate.

i dont know