I_should_have_known -

Depending on what you're looking for, "I should have known" (or "I should have known better") likely refers to one of the following popular topics:

This is a popular fast-paced trivia game where players are asked questions about things they ideally should know the answers to (e.g., "Which way does a fan turn?"). i_should_have_known

Several famous tracks use this phrasing or a close variation: How To Play ...I Should Have Known That! Depending on what you're looking for, "I should