Matt Barnes -- Beefin' With Colin Kaepernick ... Calls QB a 'Hoe'

Colin Kaepernick has a new enemy -- L.A. Clippers star Matt Barnes ... who just fired a shot at the QB on social media ... and sources tell us the animosity is very real.

Barnes went on Instagram to congratulate Arik Armstead on being drafted by the SF 49ers last night ... and wrote, "Congrats to my young boy #ErikArmstead [sic] proud of you fam. Ur QB a hoe tho!!"

Clearly, the message was directed at Colin.

Multiple sources close to Matt tell us the beef with Kaepernick goes back several years -- and stems from a situation where Matt felt "disrespected" by Colin.

As one source extremely close to Barnes puts it -- "Matt hates his guts."