At the home center when the check out lines are long, I'll purposely buy an 8 foot 2 x 4 and take it through self check out. The UPC (Bar) code is usually on the end grain. As I start to pick up the 2 x 4 to scan it, the clerk usually runs over with the hand held scan gun. The conversation usually goes like this.
HC - "Let me scan this for you."
ME - "OK"
HC - "You really should be taking this through the regular check out line."
ME - "You really should have more check out lines open."