A boner or erection that occurs in one's home, or in any other place alone. This includes when they are looking at porn or reading/thinking about something erotic. A Loner Boner can also occur when somebody unattractive is around, such as a parent. However, if you are with a girl (or boy, depending on your gender preference) and you get a boner, this is not considered a Loner Boner.

the thing that you don’t have when you’re phones percentage is over 20

An erection that occurs when standing on your own. These are entirely random.

anyone who gets a boner when alone or in a group of guys.

When a person who has few or no friends and keeps to themselves masturbates.

When she's "not in the mood".