When a person is sitting down, their lap is in a form such that another person can sit on it.
When a person stands up, their lap still exists but is not in a usable form.
"I can't until you get the hamper off of your lap."
2.) Repeating the above process of walking through a bar or club to "pick through the merchandise" for some prospective dates or tricks, etc. Sometimes known as "window shopping" (Thanks Clickboo!)
One is treated to L.A.P. when a neighbor/roommate with whom you share a thin wall, or live close enough to, has loud sex. Generally characterized as a truly terrifying experience in which the recipient of the L.A.P. is subjected to aural terrorism in the form of moans, groans, yelps, heavy breathing, bed/furniture crashing, and various other unsettling noises.
The L.A.P. I caught the other night was so bad, I could tell she didn't cum.