Magniv is kind of like ‘cool’ or ‘groovy’ or ‘sweet’ in English. A very popular word with younger people, you might not hear your friend’s saba סבא grandpa use it.
lehagniv mishehu al mashehu – to excite someone about something
When the “niv” is stressed, it means “cool“. When the “ma” is stressed, it means “wants to be cool”.
