You smell bad. Cycling and running shorts are uniquely positioned among clothing in their ability to take on an unpleasant odour within 37 seconds of being on your person. The implication of this is that if you get lazy and decide to two-jack your shorts and wear them out for a second workout, an article of clothing that normally does not smell good actually becomes toxic and requires a WHMIS label.
This is an easy rule to remember: it does not matter how long you wore your shorts for the first time (three minutes or three hours - it does not matter), they need to be washed before you wear them again. This is not negotiable.
Further, bicycles are uniquely positioned in their ability to travel over pavement at incredibly high speeds in near silence. The implication of this is that if you are approaching someone from behind and your bike is well tuned (your bike is well tuned, right?) they cannot hear you coming.
This is also an easy rule to remember: get a bell, sing a song, just do something to let people in front of you know that you are coming well in advance.
PS --> runners, the above rules apply equally to you. Wash your shorts and let cyclists know when you are passing.
That feels better. Thank you for your attention.