If the enemy is lagging, killing them is not a reportable offence. Is it 'bm'? Possibly. But if you think about it, a person who is playing with awful lag should be that more careful when laning/roaming. Ultimately, it's their choice to play with the lag (Edit: As in, they decided to not check to see if their internet is acting up, and don't bother to try restarting client to fix it possibly,) I say they're as fair game as anyone else.
That's why you don't get mad in CoD if I get killed for taking a drink of soda instead of both hands being on the controller, I'm not going to shout "I WAS DRINKING SODA QQQ" because ultimately, I decided to play the game under a circumstance that hinders me.
That's just my two sense however.