but when I see it on other people when they try to hide or go unrealized , its amusing

Always nice when your best friend pops up and shows vigorous signs of life, even if just checking out the situation.

Also great to see someone out walking, exercising, showering, or showing the natural effect of being crunched up in a small seat on a long flight.

Whether you think an uncontrolled display by, say, a high school wrestler (as in all those YouTube videos, is a hot reminder of manly equipment ("When properly viewed/ Everything is lewd" -- Tom Lehrer) or think it is funny because the recently pubescent jock still has little control over the body part that will please him most in the rest of his life, now that he has started to discover its gifts, its capabilities, and occasional physical inconveniences (ill-timed NON boners is a related but opposite problem that may be discovered at any age, though esp. among the old.)

Besides being the kind of thing that can cause merriment in others, like the sudden voice shift that may happen when a developing teen is speaking in class, there is also the embarrassment factor. Laughing or snickering can be a common result among those experiencing the temporary shame vicariously, almost as if laughing about it says (deep voice:) "Not ME."

Please see the Health and Fitness forum for a related question concerning "morningwood."