DXM and Phenibut are close at the top, but DXM has to win because the comedown is more of a wonderful afterglow and seldom is it un-enjoyable. Phenibut on the other hand... I think I'd rather be shot with a paintball, naked. Twice. At least then, the pain (so to speak) would be over with faster and I wouldn't have to go through the cycle of "Never again" but saying fuck it every so often to the lure of the amazing effects Phenibut gives me (Like vomiting :D).
Now I thought I'd share as well the worst legal "highs" I've ever had. Kids, if you're going to do drugs, please try and find something besides DPH to try for your first time. I read a "trip report" of some teenager (this is 100% truthfully SWIM, I'm glad I'm not like this) who wrote lines such as: "The truth about this drug is that it is excellant, amazing, incredable, but its very hard to remember anything after I take it.", or, even better: "When I woke up, I was upset because I thought I had slept the high off, but then I moved my legs, and they were convulsing and shaking. It felt amazing!", or, somehow even better, " I don't remember waking up in the hospital. It's like I just appeared there. The first thing I do remember is blood being taken from me. Five viles I believe. No pain, and I am usually quite squimish about those things. They moved me to another hospital, and I was moving slow, shaking, in complete ecstasy. I believe I was in a straight jacket, but I'm just not sure.".
Just stop.