Coneheading is a sexual act that involves a male (or female) strapping a strap-on dildo around their head and using it to penetrate their male (or female) partner.
"man, I was so drunk I couldn't get it uplast night, but she had a strap on so we were coneheading for hours!"
When a woman make a dominant play for commitment from a (usually unwilling) male. The purpose of this action is marking the male as property of the woman, after she claims her stake.
Alice and Bob were arguing again last night; Alice has been cocksteading ever since she found a bra that wasn't hers in Bob's bedroom.