I guess that would depend. are you close to this person, or people they may party with from time to time? ive actually put alot of thought into it and wrestled with going through with it, if this is the case. this guy i know, and am friends with -well, friends in his mind- is basically scum of the earth and a pain in my ass since the day we met. but thats irrelevant. anyways, in my specific case, this person is also a heavy drug user. hes told me that his bucket list is just a list of street drugs and other things you can use to get really high.
i agree with the poisoning idea. but if you just randomly gave him hemlock tea or some shit, the autopsy docs would probably run a few tests to figure out what it was, and bam. murder investigation.
so, assuming everything i mentioned earlier is the case, you buy a gram or so of cocaine and a nice bottle of rum or moonshine or something really alcoholic as a 'gift' or to celebrate something or some other reason you can think of. make up an excuse not to do the coke, because what he doesnt know is that youve also ground up a couple of anticoagulant pills (go for 10mg warfarin pills. they're white, so will blend in) into the coke he's getting.
what you've basically given this guy is the unholy trinity of chemical interactions. when you mix coke and alcohol, it can increase the heart rate to already dangerous speeds, which helps speed up the kicker - mixing alcohol and anticoagulants can cause a person to hemmorhage, which the increased heart rate will push out at a nice pace. but, since there's likely bleeding going on in the nose, the two are gonna make a mess. so, if it's a thing with lots of people, try to find yourself an attractive lady friend (if you aren't one already) who would be willing to take them to bed so nobody notices the red river flowing from his nose and gets the idea to call an ambulance. because that would be no fun. if you decide you can let them in on the plan, have them "pass out drunk" before or after the sex (let it be their call), and then wake up, find the new corpse, scream for theatrical effect, and then call an ambulance.
if you played your part well, it'll just look like some moronic druggy ODed, and that will be in the report, adding insult to injury.. or, well, death.
they likely wouldnt perform an autopsy or open an investigation.