Floyd Mayweather was like a human ATM at the Bad Boy Family Reunion concert in Vegas this weekend -- dispensing $100 bills to the crowd ... just because he felt like it.
Lil' Kim was performing "Get Money" when Floyd walked out onstage and began to make it rain. A rep for the boxer told us he threw roughly $9,000 in cash.
Floyd's rep says he and Kim are "very good friends" -- and he just wanted to do a nice thing.
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