This achievement can be gotten in forge (as well as all the other MP achievements that don't say they need to be in a matchmade game). Simply load up a second controller, remove all the respawn points from the map by pressing
while holding one and clicking 'Delete all of these'. Then place a hornet and one respawn point. Have the second controller kill themselves and respawn at the respawn point. Simply get into the hornet on your main account and kill them repeatedly as they spawn. It'll pop after 30 kills. :)