Identify the incorrect word usage: He felt bad about the mistake he made.

In this sentence, the use of "bad" is considered incorrect because, traditionally, "bad" is an adjective that describes a noun, while the phrase "felt bad" refers to a state of feeling. In more formal English, the correct phrasing would be "felt badly," which uses the adverb "badly" to describe how he felt about the situation. Adverbs modify verbs, and in this context, the verb "felt" is the action being performed. Therefore, "badly" would more accurately describe the manner in which he felt about the mistake he made.

The other words in the sentence are appropriately used. "Felt" serves as the correct verb form, while "mistake" is a noun that accurately describes the subject of the sentence, and "made" is the past participle of the verb "make," correctly indicating the action he took concerning the mistake.