Directly translates to "Your mother vagina." However, if you had to compare it to an English phrase it's almost like a big 'Fuck you' however it's intensity relies on the person you are saying it to. If you're saying it to your friend for example it would be perfectly okay and he/she should not get too butthurt. However, saying it to a stranger or someone you are not som familiar with could lead to your demise.

When someone goes to the gym and spends 90% of the time on their phones scrolling through social media

kus omak is a word of the language used to describe a mum. Saying that the mum your describing is very beautiful.