Deja Vu All Over Again

So you know there is security at an airport. You'd guess, then, that there are security procedures that we perform on the actual airplane. There are, and I'm not going to tell you what they are (for security reasons). But sometimes through a combination of poor planning and our own stupidity, we shoot ourselves in the foot.
Take for example, getting to Winnipeg. We had already secured the aircraft that morning, and so we boarded the aircraft for Canada. Then one of the gate agents says we have to do a second sweep because we're going to Canada. The captain argues that it's already been done. I watch him argue, glassy-eyed, because I know that no matter what he says, I'm going to have to do another sweep. While the pilot flips frantically through the manual and gets on the horn with operations, the gate agent tells me I have to tell all the passengers they have to deplane in order to replane moments later. I hand the phone to the gate agent and tell her she has to tell all the passengers they have to deplane in order to replane moments later. And let me tell you... when people get on the plane, you say hi, and when they get off, you say bye, but there's nothing you can say when they're getting off to get back on again.
Naturally, just after they finish boarding the second time, operations confirms that there is no need to deplane anybody, don't do that. So I announce to the passengers that we appreciated their patience and that Guinness was on the way to witness that we set the record for the most boardings in a single flight.