I tend to talk about the distribution name e.g.
"I use Trisquel"
"What is it?"
"It's a distribution of the GNU Operating System, made up of just free
software. It uses Linux as it's kernel"
"Oh, I have heard of Linux, my friend is obsessed with it!"
"It's not what your friend thinks. Linux isn't really an operating system, it
is a program called a kernel that lets programs control hardware. We say
GNU/Linux or GNU+Linux to describe the GNU OS running on top of the Linux
kernel."
"That's fair enough, can you tell me more about GNU?"
Etc. Many people I have spoken to are curious. They then make some decision.
It is a brief conversation. Trisqyel is a reasonable name and is not a
mouthful to say, but it is important for people to know about the
contributions of GNU Project and Linux.