As defined by Sal Vulcano of Tru TV's Impractical Jokers. Being vanbumbled is to see a family member naked.

v. collectively or individually finding someone/something to blame for a problem, as opposed to brainstorming which connotes finding solutions to a problem

n. the act of finding someone/something to blame for a problem

(from a TV ad for HD television)

When you accidentally see a family members genitalia.

When you accidentally see a family member's genitals.

When you see a family member’s genitalia. A vanbumbler is the one that shows their genitalia to a family member.