I loaded trucks at UPS during the week, was the lowly dish washer on the weekend. My truck-loading chops made me a dishwashing ninja, so I split my time on the weekend between a couple of place for lunch/dinner/special events.
In addition to no substitutions, don't send anything back that isn't "cooked right" (unless its egregious, and even then.....). You'll get your meal back along with something that's "off-menu".
I thoroughly believe restaurant staff, and not take-out places, are the only ones that truly have a tippable job. The amount of bullshit that they have to smile and take from people while serving them is insane. The 3 places in the world where you really get to witness a persons true level of crazy is the bathroom, airplane, and restaurant.