I laugh out loud, especially when I'm by myself. My wife finds it annoying, so I try to stifle it when she is around. I love laughter, and I believe it helps relieve stress.
My son (16) does it even more than me! His computer is on the main floor, and we often hear him laughing loudly. When we watch funny videos, he laughs so much we have to rewind. I find mself laughing with him when we are enjoying something together.
I also find myself laughing out loud, sometimes uncontrollably, just from the recollection of an event from the past.