A double entendre of "bones" that started on the Random Insanity GameFAQs forum. It it used when one wishes to make a joke about a person "boning" someone only to deny it and tell them that they have a dirty mind.
Person A: Did you know that she bopnes his brother?
Person B: You mean bones?
Person A: No
Person B: What is a bopnes then?
Person A: It's whatever you want it to be.