10. Why do I get unwanted erection now, as an adult? What should I do about them?

Nature, of course, doesn’t know that some erections are unwanted, any more than it knows that freckles or blush are unwanted. Unwanted erections are more common in adolescence because the teenager threshold of arousal is far lower than the adult threshold ¬–that is, it takes less stimulation to arouse a boy than a man.
Adult get these erections for the same reasons that teens do: unintentional physical stimulation, such as from clothing, furniture or a hand; "mental or emotional stimulation, through fantasy, desire, guilt, or embarrassment; urethral stimulation, because of infecting or the need to urinate.
What to do about unwanted erections? Repeating “I’ am loosing my erection” doesn’t work. Thinking of disgusting things (like the amount of money Michael Jackson makes) isn’t dependable either. You end up with sour face in addition to an unwanted hard-on.
There are several time-tested ways to get rid of unwanted erections. These include root canal, a speeding ticket, and a tax audit.
If you’re positive that your arousal system is completely out of whack, see an urologist. Other wise, appreciate the fact that your penis does, apparently, respond in a youthful, enthusiastic way. Don’t be embarrassed—that “problem” down there is just an erection. The surest way to get it down is to let it down, by ignoring it.