Found: That day so good that Ice Cube wrote a song about it
January 27, 2012
And we have competitive skater Donovan Strain to thank for that. Using two of humanity’s greatest tools, SCIENCE and DEDUCTION, Strain has pin-pointed to which day Ice Cube was talking about on his classic, “It Was A Good Day”, using clues in the lyrics and doing a little research, (ie, which days did the Lakers beat the Supersonics, was clear and had no smog, etc.) and he posted his methodology to his Tumblr. Aaaaand that day was… January 20, 1992. Trust me, the way he got to the date is more amazing that the date itself.
Thanks to Line Out/The Stranger