It's rare when a conversation about how to spend half a million bucks gets highjacked, but that's exactly what happened to Gunna when a hyped-up fan hilariously rolled by ... armed with compliments and a megaphone.
We got the "Dollaz On My Head" rapper leaving Dior in Bev Hills on Monday celebrating his 28th birthday. Dude did a ton of shopping ... as one might expect after Lil Baby gifted him a cool $100k.
Gunna was telling us how he was going to top Lil Baby's gift when it comes time to return the favor -- and just as Gunna was dishing deets on how much he was going to drop for his own bday weekend a car rolls up and steals the show.
Watch the clip ... the dude in the car paid Gunna tons of compliments. And, when our photog told the fan it was Gunna's bday -- well, ya gotta see how the fan leveled up.
ICYMI ... Gunna said Lil Baby, who he refers to as his twin, gifted him $100k for his birthday.
Gunna says he hasn't spent all the dough ... at least not yet. No word if he's saving some of it for when he returns the favor. Lil Baby turns 27 in December.