Sneak preview 

n.

1. (Communication Arts / Broadcasting) a screening of a film, or series pilot, at an unexpected time to test audience reaction before its release. Not to be confused with sneak peek.

We were invited to a sneak preview at Warner Bros. Studios!

Sneak preview by Jrskow July 16, 2011

sneak preview 

when you catch a glimpse of a large dick protruding through too tight boxers

I wasn't too sure Id I wanted to take him home tonight, but then a caught a sneak preview of the fun to come. I thought, hell yeah, im game.

sneak preview by Clare..and of course..eric too. May 19, 2004

Sneak Preview 

Jumping into some one with arms spread colliding chest first into that person while yelling “sneak preview”.

Did you just see Trav deliver the "Sneak Preview" to Adam? He knocked him on the floor.

Sneak Preview by Joe Cadena June 29, 2006