beyonce*Apparently boy band Mindless Behavior lived up, er, down to their name Sunday night at the BET Awards as far as Beyonce was concerned.

Bey was so upset at what they said about Lauryn Hill, that she changed her acceptance speech (on the fly) to honor the former Fugee.

So let’s start with The Diss — Comedian Mike Epps and the group Mindless Behavior were co-presenting the award for Best R&B Artist when Mike jokingly tried to sing.

One of the members of the group quipped, “You sing BAD … like Lauryn Hill’s tax accountant bad.”

The diss drew gasps from the crowd … and pissed off Beyonce, who ultimately WON the award that was being presented.

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But TMZ has learned … B was so upset, she scrapped the speech she had prepared and defended Lauryn’s honor instead … saying, “I want to thank all the talented R&B women that came before me like Lauryn Hill and Mary J. Blige.”

When B walked off stage, there was a woman waiting for her — possibly a BET handler — and B began to vent about the insult, saying the Lauryn Hill diss was “disrespectful” and “not cool.”

The woman complimented Beyonce for adding Lauryn Hill’s name to her acceptance speech … to which Beyonce replied, “I just felt [the diss] was wrong.”

Beyonce’s rep was called for a comment , but so far, nada.