Some British friends gave me a nickname ''Jap's eye'', is it very derogatory? I'm Chinese but have small eyes?

Question:

in case ''Jap's eye'' doesn't make any sense to you, they told me the meaning of their slang ''Jap's eye'' means ''hole in the penis'', because i often joke with them, so they joke with me too. but should I be angry with them for giving me such a bad nickname. and i'm not even Japanese, they thought i was japanese at first.
i don't mean to offend anyone here. How bad is this nickname? should i leave them? they are young of course(early twenties). have you heard of this slang?

Answer:

Basically, I like troll questions. But this is weird.
You failed our audition.