When it's bigger than u thought ((;
Or smaller than u thought )):

The act of startling someone (preferably a spouse or partner) by placing your member on top of a door handle from a room they are about to exit. By doing this the first thing they see is dangus, as soon as door is fully open you yell "dick surprise" and run away. This usually results in a loud shriek and elevated heart rate. Probably not safe for the elderly or those with known heart conditions.