"This food is terrible" merely needs to be true, and anyone can say it, even people who aren't chefs. This is a ridiculous barr that only sorta kinda sounds reasonable if you just want an excuse not to like the message or the messenger.
If you bitch about how "this food is terrible" but you do nothing to make it more palatable or order something else and instead just stand there eating while complaining and reordering and asking for seconds... The food is not terrible, and you just enjoy bitching.