Everyone knows what the phrase 'my two cents' means. Giving your two cents means offering your opinion, and often doing so when nobody's asked for it. Here, a customer has literally given two cents to the server along with their opinion.
As the note says, 'get faster cooks,' it seems that they had a legitimate reason to be unhappy with the service they received. If that's the case, though, just don't tip. There's no need to get smart about it.