A sexual act in which a male mastrubates into a bowl of rice pudding, and then gets sexually aroused as he watches the unknowing individual consume the pudding. This was a popular practice among college students in the 1980's and is still widely done in southerb europe.
Dirty Rice is a term that basically means "a shit-stained pussy". It occurs mid-coitus when you pull out of the anus and proceed to insert into the vagina and continue coitus.
Your friend awakes from a daydream to declare "last nite I was banging your momin the butt then I pulled out and put it in her vag!!" Which is then followed by an observer declaring, they call that dirty rice!!