As a feeling, being straight fire is when you're on the up and up, dropping low with your homies, making that dough, spitting that game, you know, ordinary hood shit.
When referring to an object, place, or event, straight fire means that its top notch, better than the rest, just mad niggerish in general, right up my alley.
How have you been? Straight Fire recently.
Man that club last night was straight fire, those bitches were jockin' on me so hard.