What does "negotiating with" mean here?
"Negotiating" is not used here in the traditional sense. Gordon Ramsey has used it here in an unconventional way: as a synonym for "dealing with." You can understand him as meaning that there is nothing worse than eating a muffin and having to deal with (negotiate with) a slice of pear skin. "Negotiate" is normally used to mean discuss or arrange an agreement with somebody. Ex: It is important to negotiate the terms of any contract you sign. Ex: I deal with many people on a daily basis.