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1.
A day when your morning wood remains until bedtime. A very persistant erection that hurts and interferes with your ability to have a nice day, often caused by a long night masturbating or having sex. This can also be caused by, but less commonly, shoving a long object through the urethra.
Boss: You seem a bit irritated today - whats wrong?
Worker: Im just kinda having a bad boner day, sir.
by Pooty__Toot April 01, 2008