Sources close to Blac Chyna tell TMZ ... Soulja Boy's an immature, thirsty clout chaser who was begging to get with her, and she's glad their relationship is dunzo!!!

We're told BC's anger stems from SB's response to TMZ breaking the news of their split. In a since-deleted tweet, Soulja Boy said he "just wanted to see what the p***y felt like."

Yeah, Draco really went there.

Our Chyna sources say she's happy Soulja Boy's out of her life because the tweet showed his true colors. We're told she felt his reaction was the lowest of the low, and utterly ridiculous.

As we reported ... Soulja Boy was super romantic and sweet while lavishing Chyna with $20,000 in gifts during a Valentine's Day shopping spree ... but it appears he left his manners in Beverly Hills.