For this achievement you need to hogtie an NPC and put him on the tracks and wait for the train to crush him. In order to hog tie an NPC you need to get the mutator first and you get that by finding ten different trophies. I will leave my video on where to find 20 trophies below as it is easier using video than explaining where to find 10.
Once you have the mutator equipt stand next to an NPC, then press y to release a cable tie. Your NPC will now be hog tied and you can now lick the NPC to take him to the track then once placed on the track wait a few mins and he/she will be hit and your achievement will pop.
If you need any more help or would like a video guideI will leave my video guide below.