when a man gets an erection and gets sexually excited.

When you eat dirt for the first time and leave your family to build a shack in the woods

A creepy guy, reminiscent of Woody Allen, who takes much too much interest in hugging, playing with, and taking nude pictures of, small children. Especially a family member who has these tendencies. The ultimate example of this is marrying your almost-adopted foster child who you photographed nude for several years.