Your first bad movie.

[Mr. DS]

I don't recall exactly which one I saw first but there are a few that come to mind. 
Return Of The Living Dead and Children Shouldn't Play With Dead Things come to mind.  They used to be on Saturday afternoon along with awful kung fu flicks.  I used to watch them a lot growing up.  My first exposures to horror were Jaws, Friday The 13th and Poltergeist.  My brother had a laser disc player and we'd watch them frequently. 

[Castroph]

Monsturd was my first bad movie, it was so crappy and terribly done that it made me bellow out with laughter each time the monster appeared.

[Joe the Destroyer]

Jeez, there are several that I can accredit as being the first.  Friday the 13th part 3, The Prey, and Swamp Thing are all likely candidates, as they all essentially got me into bad film.  I was about 3 or 4 when I saw these movies, and still remember watching them even when I was that little. 

Hell, I think King Kong vs. Godzilla might even predate those. 

[GLKnight]

Ninja Wars.

Seriously, I was three years old, with nothing but Disney, Transformers and Anime until then. Same tape had the Advetures of Lion Maru, a kaiju/sentai ninja show, Captain Future, and The Dragon Vs. Needles of Death. Then they allowed me into all the other 500(!!) VCR cassettes we had.

Not to mention I first saw a Troma movie at the age of 6 (Toxic Avenger baby!). Man, I miss shows like USA Up All Night...

Let's just say I got a head start of all my friends.

(My favorite example: "What you haven't seen 'Meet the Feebles'? I saw that when I was 9!")

[Justy]

It's really hard to look back and see which one was the first. I watched a lot of movies when I was a kid. If I have to guess, perhaps The Day of the Triffids. Although my earliest favorite was Godzilla vs. the Smog Monster. Those psychedelic scenes were awesome.