Sinking Your Own Battleship

Any action taken by a person looking to have a relationship with another person, that effectively ruins their own chances of having said relationship

Guy 1: "So I was really into this girl, but when I walked up and kissed her on the cheek, she freaked out."
Guy 2: "Way to go man! Talk about Sinking Your Own Battleship!"

hung by my own noose

When something backfires; when you forget a prank you did and it happens to you.

"Alas! I've been hung by my own noose!" Said Angle after she turned her sister's hairdryer on, forgetting she put flour in it previously and ended up looking like a fool.

Legend in their own pants

A person who believes they have a big dick or twat while projecting a false reality of grandeur or self-importance on to others.

Some people are a legend in their own pants because they tell people they live the high life while living in a dump.

twat who thinks they own everything

lochie.

lochie is the twat who thinks they own everything.