My personal experiences when demoing my car:

The mention of two 15s gets respect from the loud crowd which is 95% of the people around here. The other so called "SQ" guys look down on them before hearing them, assuming I'm like the other 95%. It's gotten to the point of being annoying, EVERYONE wants to hear what the 15s can really do, even though I keep it a little on the bass heavy side as is. I've cranked the gain real quick for a few people but I don't bother anymore to throw the tune off for some idiots.

Having 10s in the doors gets the same reaction. The best solution is to not tell anyone what's in the car, at least not until after they've heard it first.

When you try to explain what the processor does, they can't get past their own "surround sound" assumption. Trying to explain a stage is pointless.

I've learned that most people quantify a good system by how much treble and 40hz bass it produces. It can sound extremely good and realistic but apparently ear bleeding treble is what they're looking for to show how "clear" it is.

That brings me to my next one... When demoing others' systems...

Infinity speakers. I think 90% of the "badass" systems I've heard have infinities and bottom of the line Kicker subs. No vocals, no identifiable instruments, everything blends together in this mess of screeching treble along with the usual overly boosted 40hz from the bottom of the line Kickers powered by a boss amp. Shit is the only way to describe these things. I want to poke my eardrums out every time.

I let a guy who has a system like this adjust mine however he wanted. I let him go to town with the MS8, every adjustment it had and lo and behold, my Dyns sounded an awful lot like his Infinity system when he was done. I was amazed, people actually want their system to sound that way.

I guess this is more things I don't like when listening to or having other people listen to my system but there have been some insanely ignorant things mentioned, most of which I try and forget as quickly as possible. I'l try and think of some more. There have been several times I almost started a topic like this one after hearing someone's car.

The only one I can think of off the top of my head which isn't that bad compared to most, a local shop said IB can't work, that it's impossible.