Friends hi-fi system not very good, what do you do or say?

So you're going over to someones home and they give you a tour and they have a hi-fi system in a room. And while visiting of course they turn it on for you not knowing that you have a very nice system in your home and you notice immediately it's just not very good.  But then you're used to the very in you're listening experiences. So what do you do when they ask you what you think?

Do you say sounds really good?

Do you make suggestions?

Do you feel a desperate need to tell them about your system?

Personally, I try not to mention any details about my system. If I'm driving around in a Lamborghini I would prefer to be invisible so I don't get stared at when I get out of my car. If they had a really nice system with interesting components I would probably mention a few of the things I have and then we could bond with our common interests.   Ideally, it would be cool to be in the presence of someone who knew a lot more than I did and a real learning opportunity.

Audio systems tend to be private affairs I guess.  I don't necessarily want to hang out with someone and listen to tunes. Those wonderful College days where it made a lot of sense are long gone.