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3.
When your penis persistently peeks through your underwear fly, regardless of how many times he is readjusted, thus increasing the risk of tip zipper rash.
Hold on a second I need to adjust my drawers. My junk keeps playing a shadowy game of penile Groundhogs Day, you know,... I've been cruising at periscope depth all day...
by willisdwaynetwayne December 26, 2009
 
1.
When a fresh a deuce is so large that it breaches the surface of the toilet bowl water, exposing the tip to air.

The toilet bowl is designed to use water to contain the terrifying smell of fecal matter. Naturally, when a load is large enough to reach periscope depth it stinks up the bathroom something terrible, requiring a courtesy flush.
"Whoa dude, did you just dump all of Bombay in this bowl? My fuckin nose is going to fall off"
"Sorry after all that built up sushi that dump reached periscope depth"
by Broham Brosef March 01, 2008
 
2.
n. 1. when you are in a body of water (tub, hot tub, pool, etc) and you are floating at a depth such that just the tip of your penis breaches the surface of the water
{to one's friends in a hot tub}
"i'm at periscope depth"
by J.Dizzie March 01, 2012
 
4.
The result of a morning chubby, the tip of one's wood will break the surface of the underwear as though to take a look around. similar to that of a submarine periscope.
"holy cow do I have to pee, but i'm at periscope depth and could take my eye out if I try.
by DickTurman March 07, 2011