I went for a ~10 mile ride on a local trail with my mom, who hates mountain biking - even more after that. We averaged about 5mph, I almost got frostbite on my hands, and she wiped out in some loose sand and the bike landed on her leg, causing a bruise.
Oh well, it was fun...

I love 'goofing around' in town, the route I love to take when possible starts up at the top of this really long, fast hill, turns off onto a side street, goes along a somewhat perilous trail alongside a cliff, then there's an area of dirt jumps and hills, you can fool around there for a while, jumping and dropping a bit, then ride to the park a few miles away, ride on the skate park if you feel like it, do some stair drops, and just have fun

Note: This ride almost always makes me feel like buying a new bike - not because this one doesn't do, but because riding just seems so worthwhile afterward