These wouldn't stop me riding with anyone, but my personal no no's
Incorrect size of zip-tie usage, an 8mm wide zip-tie really isn't needed to hold a disc hose in place. While we are at it, all heads but be rotated out of view and if in a row all heads must start from the same side and must all be aligned to each other. And they must be black, coloured zip ties do not look good.
Gear/brake hoses must be cut to the appropriate length. Just enough spare but without flapping in the breeze.
Seat QR must always run in line with the collar.
Stem and seatpost should match.
Brake lever bite-point must always be after about 5mm of lever travel.
Presta valves only. Front and rear stems should be of same length and have the same valve cap.
Headset spacers should always be under the stem and must all be of same type. Exceptions allowed for the 'just built' to check stem heights.
Accessory add ons should be kept to a minimum, preferably none at all. Mudgaurds never used on dry trails. Items left on from a previous ride which aren't needed on this particular ride should be removed.
Helmets. Selfishly I personally don't want to have my ride ruined by someone else falling off and bumping their head and needing to wait for an ambulance.
Lycra shorts and baggy tops (baggy shorts fine with lycra tops).
Baggy clothing on a road bike. You don't look like a real MTB'er at heart, you look like a prat. Just as someone turning up to play cricket in football kit would do.
Grips must always finish at the end of the bar, not hanging over the edge or mounted inboard. Endcaps must always in.
Distance from end of grips to brakes and/or shifters must be equal on both left and right hands.
QR's must be Shimano.
