Entheogenic experiences, like life itself, are what you make of them.
I can honestly say I've never had a "bad" trip. Now I've had a few downright scary trips, particularly some LSD, DMT, DPT, and Salvia divinorum experiences I can think of. And I also kinda "wigged out" once on 5-MeO-DiPT and once on 4-Ho-DET. Oh, and one baby woodrose seed trip, and a few morning glory seed trips, were scary. I had taken way too much on each of these seed trips and my ego went into “resistance mode” against my control. The time when I took too many woodrose seeds I thought I was going to die in fact. Truly believed I would. I'd never felt in fear for my life (haven't since either) so it was very terrifying. Powerful seeds they were!
Only on my second LSD trip (about 10 years ago) did I ever take a psychedelic in a really uncomfortable setting. This was my first real "acid experience." The first time I ate a "hit" of LSD there was only, maybe, 50ug of LSD present. However the second time I took LSD I got a full ego-smashing dose. I definitely took above 250ug and it was enough to shatter my ego like it had never been shattered before. Previous morning glory trips were powerful, but they never took me that far. LSD has an ego-shredding capability that no synthetic indole I’ve tried, except perhaps non-orally consumed DPT, can touch.
My first real LSD experience took place at a friend's house and an unexpected amount of people showed up that I was not anticipating. Well, I simply was not ready to have my head split open like that with so many people around me. I became very confused, and just generally uncomfortable.
I started drifting in and out of my body/usual space of consciousness. During much of the peak, I'd forgotten I was even tripping, where I was, or what I was doing. But it also would come in waves at times. When my ego returned to my body I'd fight the experience, which resulted in an extreme raw state of fear. And then I'd be swept out of my body again and there was little ego to put up any resistance anymore; only enough to retain memory of the experience. I remember at times not knowing who "I" was, yet I remember the whole trip with complete clarity.
But by the time the peak was over, I thought it was the most amazing thing I had ever experienced! Well it was up to that point. When "I" left “my” body, the states of consciousness experienced were beyond what I knew existed, or possible. I was in shock and awe for a long time after my first real LSD experience and realized/experienced a lot of things previously considered to not be possible. It really "opened my eyes" and began my long road (which I am still on) of spiritual discovery.
But none of those trips were bad trips. I grew in one way or another from each of those experiences, however scary or unpleasant they were at the time. And if you learn from a trip, and grow from it in some way, then I can't call that a bad trip even if it was frightening during the initial experience.
It also helped that I always had these experiences in good settings and had nurturing and loving people with me to be there. Even that LSD trip I talked about, my best friend was there and tried (when he wasn't too gone as he was also tripping) to keep me calm. I've always been careful about where I trip, especially since that LSD experience, and who I am with when I trip.
The big thing is control over your setting. The first thing I learned when I started reading about psychedelics was set and setting. Be in one you have control over! I guess I’ve only broken that credo when I've tripped at concerts. I don't have control over my setting then. But every concert I tripped at was either a Grateful Dead/post Dead entity, Roger Waters (of Floyd), or Dylan. And I was not the only person tripping (I think 3/4's of everyone was tripping at that Water's show) so I did not feel like I was in any danger of attracting unnecessary attention to myself. Those who have been to a Dead show know that almost anything goes! And I always had a sober friend to watch over me.
I guess if I got arrested while tripping, that would be pretty bad. Or if I lost a limb or my penis in a strange knife incident, I’d have a bad trip. But none of those things have happened to me so far!