Last night I my electro-rock band had our first gig at this nice place in San Jose called Avalon, and it went really well and we had a great time. However, our set started with a little problem...
In the mad rush to load all our equipment on stage after the prior band, I was sweating like a dog and completely paranoid that I would forget something. We're a trio, but our frontman uses two keyboards and a guitar, in addition to our drummer using an electric kit and me with my spacey pedals (yeah, we have a lot of toys...)
I do the rapid sound check - making sure that I have volume equity under control whenever I step on my big muff - and right before we start, I realize that the -10db button is pushed in on my GK Backline 600. "Crap! I'm not gonna be able to hear my cab through the earplugs!" I quickly turn it off and think "The house has a direct out, this isn't gonna affect the mix, right?"
WRONG!
We play the first song and I think "Wow, they put a lot of my bass in my own monitor, that was nice of them

..." The sound guy comes running up in the middle of the song:
Me:

Him: You're too loud!
Me: What?
Him: YOU'RE TOO LOUD!!!
Me:
Apparantly I was completely crushing the entire venue with a tyranical monstrosity of crunchy rumbly-ness
I do my best to left-hand tap my part while I adjust the volume on the head, but to no avail. I manage to fiddle the gain knob and my on-board volume knob enough to get it under control.
For the entire evening I am second-guessing everything because while I would usually set on-board volume at 9 o'clock clean and 6 for FX in order to have volume equity, it's now like 2 and 4..
Everything adjusts fine after the 2nd song and everyone says that we had a good mix from the third song onward. Phew! I explain to the sound guy afterwords that I've never used the direct-out on my amp before, to which he gives me this look that says "I'm refraining the urge to slap my forehead right now"
But halfway through the set, the sound guy treated us to a little light show as a result of the rocky start -
http://www.flickr.com/photos/mike_kong/3851593165/
Lesson learned: Don't push buttons after sound check! -10db is my friend!
EDIT:
In retrospect, here's page 7 of my manual -
"The Direct Output signal is only effected by the -10db Pad, and Tuning Mute controls."
oops... :P