2 Chris King headsets – constantly worked loose, clicked and creaked, and started chewing a nice groove into my steerer tubes. Both had damage to the bearings from being ridden loose. Evolution Imports would not offer warranty support but kindly offered to sell me new ones despite both being less than 2 months old. Replaced with FSA Pig Pro at £30 each and no problems for 2 years until bearings went rough.
Shimano XT disc hubs – the rear hub would not stay tight, no matter who tried to set the cones. Annoying, as I’d had 2 sets of wheels built with these hubs.
Specialized All Condition Armadillo road tires. Yes, they were puncture “proof” as you’d spend more time in the hospital than riding, as they were super slippery death treads – watch out for wet roads, drain covers or cobbles.
Specialized Tricross bike – rubbish on the road, rubbish off road. Most pointless bike I’ve ever owned. Sold on quickly.
Tioga XXL DH saddle. Land slightly wrong and the rails either bent or snapped. Went through 5 as local shop selling them off at £5 each, before seeing error of my ways.
Azonic DH saddle – with aluminium alloy rails (!!) = snap. Wades were kind enough to warranty 2 and then gave me a refund on the 3rd.
Marzocchi Junior T fork – worked ok until you went over 20 mph and hit some bumps and then it turned rigid. Sold and replaced with Super T Pro which was a revelation to say the least.