This word seems to have enjoyed a resurgence of popularity recently, usually as a contemptuous statement that someone has "beclowned himself." It is indeed a long-attested word, rather than a newly coined word or a nonce word. From the OED entry on the prefix "be-":

5. Forming trans. verbs on adjectives and substantives, taken as complements of the predicate, meaning To make: as BEFOUL, to make foul, orig. to surround or affect with foulness; ... BESOT, to turn into a sot. In modern use, nearly all tinged with ridicule or contempt ....

b. With n.: bebaron, to make into a baron; bebishop, beclown ...

1609 ROWLANDS Crew Gossips 24 O wretch, O Lob, who would be thus *beclown'd?

Everything old is new again.