The key to this man's mistake is hidden in the mistranslation of the negative here. There is a negative of subjective opinion here indicating that the offending man, did "not want" to have the appropriate attired, (see article on the negative here). In the KJV, it is translated simply as "not," and in the NIV it is totally eliminated, replacing the negative and the verb with the proposition "without." This makes the king's accusation regarding the man's choice invisible.
The "wedding garment/wedding clothes" is also confusing. The word means "clothing for a wedding," not referring to a specific type of garment.
This final word is the punchline, a verb that means "was muzzled," which probably sounded as funny then as it does today. Jesus only uses this word four times, twice to address demons and twice as a punchline.
Christ's Words in Matthew as a Guide to 40 Days of Prayer.