"Teen Mom 3" star Briana DeJesus' baby daddy let a little thing like a weed citation snowball into a warrant for his arrest ... all 'cause he never showed up in court.

Law enforcement sources tell TMZ ... Devoin Austin was arrested Friday in Orange County, FL on an arrest warrant that was issued way back in August 2016.

The warrant stems from a traffic stop when cops cited Devoin for possession of weed and drug paraphernalia. He was supposed to be arraigned a month later, but never appeared -- hence, the warrant.

He could've gotten up to a year in jail or $1,000 fine for the original misdemeanor.