Chief Keef -- Weed-Sniffing Security Guard Was a Fat Racist

17-year-old rap sensation Chief Keef is crying RACISM -- telling TMZ the "fat ass" hotel security guard who busted him for smoking weed had it out for him because he's black.

TMZ broke the story ... Keef was arrested in ATL for disorderly conduct after a security guard at Le Meridien Atlanta Perimeter Hotel called 911 this week ... claiming Keef was "rolling marijuana" inside his hotel room with two "black male" friends (one of whom was fellow rapper Tray Savage).

Here's Chief's account of the situation:

"So me and my homie Tray Savage was in the hotel room chillin' when some fat ass security guard started knocking on the door talking about he needed to fix a water leak."

"So his ass walked in and started looking around at us and immediately gave me the racist look then started talking sh*t to me."

"I told him, 'I thought you wanted to fix a water leak?' Which he obviously lied 'cause there was no water leaking."

"Then he immediately started talking sh*t to us. He told me that he was going to call the police on me so I called him a bitch."

"He kept saying how the police about to be on their way to lock me up so I blew smoke in his face and pulled out 30 racks (white person translation: $30,000) and said I got the bond money -- there is more where this come from."

Keef says he felt the security guard was "racist from the moment he walked in the room. The way he looked at us was a racist look."

As we previously reported, the security guard told 911 he was only on Keef's floor to track down a water leak in the hotel ... when he got to Keef's smoke-filled room, the rapper let him inside "as if it doesn't even matter."

FYI, the security guard (who is white) has already denied racism accusations -- and called "TMZ Live" this week, saying he was simply doing his job when he called 911 ... because marijuana is illegal.