I braved Costco today on a bad day... it was the first day their new coupons were valid, AND it was a federal holiday where some workers and most schoolchildren had the day off. I went into it with no timeline, a totally relaxed and zen approach, with a commitment to be genuinely nice to anyone I interacted with.
Success! Sure, I came home drained and was emotionally unable to make the *other* errand stops I intended to complete, but I had a real smile for every employee, I let everyone push their carts in front of me, I never took the last sample from the tray. Even in both the parking lot AND the gasoline line I smiled and held open the metaphorical door for others.
I don't like to let pithy proverbs win, but it's true today: it IS all in your attitude. And when going to Costco, be prepared for the worst, and when it arrives, greet it with a smile -- and plenty of time on hand.