Oh god, I know what that's from too.
I remember a certain fanfic about a certain somewhat hapless trouble-seeking commisar, which starts with him making a bra-raid on a Adepta Sororitas compound, blaming said raid on fellow commandos, later in life being put in charge of a penal regiment, blowing up a huge ork compound with said penal regimen, witnessing the death of the penal regiment after running away from the ensuing waaaagh that was chasing them, meeting the warboss 1 on 1, killing him with a melta or krak grenade which he put in said warboss's mouth, with his hand, with predictable results, and befriending a space marine chapter (was it salamanders or something?) and getting what basically amounts to "avoid-inquisitorial-questioning-for-free" card (later he became an inquisitor himself if memory serves?).I think his name started with M or something, i'm not sure.
The "DRIVE ME CLOSER I WANT TO HIT THEM WITH MY SWORD!" part was somewhere around.. dunno, the raid on the ork compound, before it blew to all hell?
if somebody has a link to that fanfic, i'd be grateful.