The two words translated as "wedding garment" means "attire for a wedding," which is not the same thing. Jesus used the term in much the same way as we would describe someone wearing their "Sunday best." The minimum requirement at the time seems to be simply to have clean clothing. Again, like wearing your Sunday best, the idea is to show respect to the host, the other guests, and the event. This lack of respect is the man's crime.

The ending of the verse is a joke. The verb translated as "put on/wearing" and "garment/clothing" are the noun and verb forms of the same root, creating an alliteration. With the negative in between, this also creates a contradiction. The sense is something like "not having attired himself in attire." If we imagine that Jesus pausing here, the audience hears that the man wasn't wearing clothes, generating a laugh, after the laugh, Jesus adds "for a wedding," on the end to reverse the idea, catching the audience jumping to conclusions, something Jesus does commonly.