I stole the Subway Employee's Manual

Here is an excerpt:
It is our goal to screw up every sandwich we make. Long-time customers realize this and will watch you like a hawk to make sure you don't throw on anything they don't want. Rise up to this challenge! The best time to sneak on unwanted food is when they turn to the register to pay.

• If it appears the customer is in a hurry, throw on a handful of olives. It takes forever to pick them off and the customer will just accept the sandwich as-is, rather than wait.
• If there is a long line, try oil & vinegar. It is impossible to pick off, the sandwich is ruined, and the customer won't want to hold up the line to have a new sandwich made. Warning: this is an advanced maneuver! You need to pick up the oil & vinegar bottles, invert them and give the sandwich a good soaking in about 0.5 seconds before the customer has a chance to say anything.