Is it necessary to write 'of' after 'off?"bounce an idea off of you"
Hi, Linkway,In general, "...bounce an idea off you..." is correct and adding "of" is just a matter of preference or style and does not change the meaning.
I think whether people say "off of" varies a lot by region and by education level.
In ordinary speech, either would be unremarkable.
Personally, I tend to use it in very few circumstances, eg:
I need to get this coffee stain off of my white trousers.
(I don't know why!!!)