When you send somebody a message over AOL Instant Messenger (or other IM service), and it causes them to send half of what they were in the middle of typing to you in a message. Also used to describe when the "your buddy is typing" indicator comes up immediately upon sending a message, meaning that the text typed in the IM box is not really for you.
12:20:01 SomeGuy123: Hey. what's up?
12:20:01 ThatChick234: nd.
12:20:10 SomeGuy123: HA! Aim Sniped...
12:20:16 ThatChick234: very funny.
The Expert Urinal is the short urinal in a row of normal urinals. They are intended for short people and children. Everyone else sees them as experts-only, due to the longer shot and possibility of splashback.
I'm just going to wait till one of the other ones clears up, I'm not taking my chances with that expert urinal.