bash up

[samfat33]

I will bash you up means I will hit you hard.
Can we use "bash up" in normal conversation with a friend or a student?

 

[David L.]

"bash" means to hit violently hard, but "to bash up" means repeatedly hitting the person until they are just about helpless on the ground with their injuries.

If you wanted to say something equivalent, but in fun, because he has been teasing you or something:
Say that again and I'll flatten you.
(This requires a tone of voice that your friend will recognize as being mock angry, but definitely not a hostile voice or with fire in your eyes!)