The penis is used for two jobs, peeing and sex. When your  penis is erect, you can’t pee easily because a muscle closes the bladder  off. The shape of an erect penis varies. It usually curves upwards  slightly, and may point to the one side. Erections (hard-ons, boners,  stiffies) occur in males of all ages, including babies and old men).

Erections can come and go without warning. They can happen at a  moment’s notice, sometimes in embarrassing circumstances. And they can  vanish just as easily. Alcohol can cause an erection to droop. So can  fear of being laughed at, of coming too soon or of causing pregnancy.

During an erection, more blood flows into the penis than usual  and less blood flows out. This makes the penis becomes larger and harder  and it stands out from the body.