Any good witty come backs to "are you scared?"?

This is a good comback. But it is a mixture of body language and verbal threat display.

Basically, you pretend that you are trying to convince that you are scared.

And you say to them "yes, I am scared, I am extremely scared,(and then you start yelling this like you are about to go crazy) PLEASE DON"T HURT ME I AM SO SCARED OF YOU RIGHT NOW PLEASE DON'T LET THIS PERSON HURT ME, SOMEBODY HELP ME". All while you are doing all of this, take a step forward towards them and get uncomfortably close.

This will not only scare them, but it will create confusion in their mind. While it may not cause them to back off, it will cause them to hesitate. This will give you enough time to either run or attack.

"No but your mum was scared of your dad walking in on us last night"

only of that ghostly reflection over there....

"no, cause im ready to stab anyone"

"Scared I might kick your ***"

"nah i only peed myself"

my tee..e,e,the flew out since you ask.

"Are you scared?"

You - "Yes, I just sh*t my pants"