Use rigs 10-15 times, never shared a rig with anyone but my gf though, and we were both disease free and in a very close relationship, and also triple bleached the needles when reusing. Using a rig more than once is incredibly stupid, but the needle exchange is a ways away and the times aren't always convenient. No excuse, but do it anyways.
Shoot coke when my hand was trembling uncontrollably
Get frustrated at not being able to find a vein and just doing the shot IM (risk of access/infection much greater than with IV)
Shooting pills like ambien, dexedrine xr, adderall, ritalin, oxycodone, etc. with just a cotton filter.
Cotton shots with old dirty cottons, got my girl nasty cotton fever once.
Taking untested rolls- gave myself a bad trip eating BZP pills on acid once.
Taking random powders found in baggies on the ground of festivals/raves, though I was always pretty certain what they were.
Shooting up in public places like train stations because I couldn't wait 40 mins to get home.
Eyeballing doses of RCs like 5meo-MiPT, 2c-e, 4-aco-dmt, and worst of all phenazepam
Mixing benzos with alcohol or with opiates (phenazepam and oxycodone nearly killed me)
Shooting normal sized doses of new batches of heroin without testing a small amount first, resulting in a severe OD, I think the H was cut with fentanyl- fortunately narcan was on hand from the needle exchange and my girlfriend saved my life with it.
I have witnessed someone with a cast on one hand try to hit himself with a needle used at least 15 times, he could barely hold the needle with his broken hand and it was so dull it could barely break the skin, I finally had to do it for him because I couldn't watch him digging around in his arm anymore. Took me another 4 or 5 attempts but I got a vein faster than he could have, it was disturbing to watch.
Used opiates/downers in high doses alone when nobody was around to check on my breathing/that I was ok.
Shot K+Heroin in the same needle, also MDMA+H, Cocaine+H, Hydroxyzine+H. K+H is the scariest though, because of the immediate K-hole, which looks like an OD, its hard to tell if the person is just holing out or ODing.
Reused cottons 10+ times, used water that had been sitting out for too long (always run out of the needle exchange sterile water too fast), general sloppy IV practice, though I am careful when I have all fresh supplies, and I do always swab with alcohol before and after, and bleach needles before reusing (most of the time)
Huffed computer duster a couple times, using that ever even once is totally retarded and completely the opposite of harm reduction.
Mixing too many drugs and getting too fucked up, not including weed which was in all of them: MDA pill+3.5 tabs of hoffman blotters + too much ketamine, 150mg oxy and 20+mg of phenazepam-also did many pharmaceuticals and cocaine during that phenaz binge, half oz of K in one week mostly IV some snorted +dope+coke, PCP+K+MDMA, 3 tabs of acid + 1-2g of K+250mg pure MDMA crystal+nitrous)
Copping Heroin, coke, crack in the ghetto as a white boy sticking out like a sore thumb to both cops and people who want to rip you off, taking the risk of getting fake/dangerous drugs (for example the fentadope I ODd on, or the chunk of clay I paid 200 bucks for), Risking getting robbed or physically injured, I have had friends robbed at gunpoint doing what I did on a regular basis for a while until I got my legit phone hookup.
Admitting wrongdoing/drug possession to the cops and allowing searches when it was clearly in people's best interests to not do so--the biggest harm from drugs comes from its illegality, and knowing your rights is a huge part of harm reduction.
Not to dockside, but I have also taken excessive doses of drugs like 400mg or more of ritalin, hundreds of mgs of vyvanse and adderall, and over 9g doses of gabapentin, quarter gram IV shots of K, half gram shots of H, quarter g shots of coke (probably not the top of the line though), over a gram of MDMA in a night, up to 3.5g of k in a night, smoked enough PCP that I was 100% convinced that god was beaming messages into my brain and that I was a prophet as great as moses.
Going to legally ordered drug classes severely intoxicated was also probably not in line with harm reduction philosophy, also going to college classes on K, opiates, weed, benzos, meth, pharm stims, MDMA.