Bookmark cum is when you are reading a book and instead of using a bookmark you simply cum on the last page you were reading. The one issue to this method is you may not be able to open the page if the cum dries and you wait too long so be fast.
My teacher told me to mark page 47, but since I lost my bookmark I whipped out my dick in front of my entire english class and made a bookmark cum
Where someone cums in the butt of someone, who then farts and the cum creates a bubble out of the arse hole; just like blowing a bubble with bubble gum.