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An erection that results from being tired or half asleep, as opposed to resulting from sexual arousal.

Also known as eight o'clock cock or early morn horn, a tired-on most commonly occurs when waking up in the morning, and may be the body's way of inhibiting bed wetting.
I fell asleep on the bus. When we arrived I couldn't stand up because people would have clocked my tired-on.

This is a nice cup of tea darling, yawn, what time is it? Would you mind joysticking my tired-on a little for me?

I had such a tired-on, I had to sit down and bend it to have a wee.
by joops April 05, 2008