In Spanish, the use of reflexive verbs like "sentirse" (to feel) is often employed to express emotions or states that involve a person's feelings or perceptions about themselves. In the phrase "Me siento como un idiota vestido como payaso" (I feel like an idiot dressed up like a clown), the reflexive pronoun "me" is used with the verb "sentir" to convey the subject's internal emotional state.

Even though "idiota" (idiot) is a noun in this context, the reflexive construction emphasizes the subjective and emotional nature of the feeling. It's not just a statement about appearance; it's about how the person feels internally, as if they are embodying the described state. This construction is common when expressing personal emotions, states, or conditions.

So, in summary, the reflexive use of "sentirse" in this sentence adds a layer of subjectivity, highlighting the emotional experience of feeling like an idiot dressed up like a clown rather than simply describing a physical appearance.