I haven't in quite a long time, but back in my more wreck-less days I would when the coke was available. I remember one occasion I was doing shot after shot of just coke. I didn't want to do it all but I couldn't stop myself... I thought maybe I could try to do a little bit less each shot, sort of ween myself off of it and maybe ultimately not crash so bad but noooope. Fucking impossible, and by the time all was said and done boy were my arms fucked. First numb of course, then bruised and sore. Decided never again would I do coke without heroin, either together in the same rig or at least precooked and ready to go immediately afterwards.
Still I can recall at least two occasions where I did speedball, felt the cocaine a bit too intensely and wound up running outside- one time in the freezing cold without enough clothing on (as if I could feel the weather anyways)- as I called a friend on the phone frantically, having to explain to them: "I just fucked myself up too much, man! I think I might have put too much coke in the spoon! will you stay on the phone with me a few minutes and just call 911 for me if I go out??". Of course I survived with no medical intervention necessary, but looking back to those experiences makes me think twice about doing something like that ever again.
Not even that though. Ever danced while robotripping? The robot?! 
