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."