A way of saying "I don't know", as in "fuck knows"

sexual intercourse with the penis into the nostril.
sexual intercourse with the nose into the vagina.

sex performed between a gnome and a normal human in which the gnomes penis is too small to fit in any of the regular sexual orafices, so is instead placed in the nose

originally developed in neolithic times, nasal sex did not come into popularity until the recnet body modification craze whereas people were more inclined to enlarge various cavities of their bodies.
the penis is inserted into the nose, and thrusted until one's thick hot jizm spews onto the receiver's brains, known as getting some "hot brains". typically those of african, italian and/or jewish descent are popular within the nasally sexual set.

To stick your finger up your nose and repeatidly doing motions to get a booger. In too hard motions, bleeing can occur.

The act of sexual relations involving the nose

When a woman swallows seamen and chocks and ends up spewing it out her nose