what idiom is used?

[fatibi]

what idiom we use when we hear or see something so amazing that our hair on our arms stand.

[MrPedantic]

You can say "it gave me goose pimples" or "goose bumps".

If the location of the hair is immaterial, you can say "It made my hair stand on end", of a terrifying situation; or "it made the hairs on the back of my neck stand up", in either a positive or negative context.

Best wishes,

MrP