An infinitive phrase is a group of words consisting of an infinitive, a modifier or the use of pronouns, direct objects, indirect objects or complements of action or state expressed in the infinitive.
Fastidious refers to someone who is meticulous, demanding, and difficult to please, especially in regards to food, taste, or standards.
Inflammable: This word means capable of being easily set on fire or ignited, and has no relation to being hard to please.
Incorrigible: This word means someone who is unable to be corrected or reformed, often in a playful or mischievous sense, but doesn't necessarily imply being hard to please.
Deteriorate: This word means to become worse or decline in quality, and has no relation to being hard to please.