Anything XTR on A Townsend or Apollo.
Rising a British Eagle Boss during the hours of darkness.
Suspension forks on non geometry corrected HT frames.
Triple clamps on frames never designed for it.
Any type of grip shift, unless you have a medical reason for such a system.
Labelling stuff as NOS simply because its still got a bit if a shine on it.
Exposed seat tube long enough to be confused for a 2 wheeled lamp post - just but a bike that fits.
Toe straps and clips, even if they are historically correct.
Girvin Flexstems - they may have been the must have back in the day, but they're still crap.
30 year old alloy frames - go read up on ductile limits.
Any Marin post Zolatone.
Paper thin Selle Italian Turbo saddles for £50 - they were a tenner wen they hit Hellfrauds shelves in the late 80's, and they weren't all that back then, never mind with 20,000 miles on them.
Stupid asking price for irredeemably scuffed crap just because its XTR.
Sting back cycling mitts.
£500 of Ringle on a £100 bike.
Paper thin rims described as 'anodising barely worn'
Early full suss.
I could go on, but apart from the list being inexhaustible a lot of hear strange peccadilloes are strangely fashionable in Retro MTB quarters today, so is be getting death threats.
You do realise that this is making a comeback with the SRAM XX1 system??