Assuming that the italicized word is querulous the definition could be impatient.
Explanation:
The question is not complete since it does not provide the options to answer it, here are the options:
A.excited
B.anticipatory
C.impatient
D.short-sighte
E.narrow-minded
F.participatory.
The sentence gives a context where the subject is in a situation which is not pleasant at all, and as it says that according to the pass of time they became very querulous, it means that they became more unhappy with the situation and being in a restaurant you can say that the word is equivalent to the synonyms complaining, critical or discontented which makes impatient the best description.
