Drafting

I confess, I am one of those lycra-clad, carbon-riding geared-bike riders. And yes I ride in groups. There is a 30% increase in efficiency if you are on someones back wheel so you can go further or faster, or you can tow a less strong rider. It is important once you get over 30 kph, where most of your effort goes into overcoming the wind resistance. If you touch, then it is the following rider who loses control, falls and generally does a collarbone. The lead rider might notice a small tap, before hearing the screams from behind. Always a good idea to let the lead rider know you are on the back wheel if you want to tag on so they can have a choice to agree to giving the tow or not.
My fixed ride is underway.

If a rider pissed me off on the way back home, (I was a right little prick when I was 18) ... What I used to ride up until I was just about to touch his rear tyre then just skim it so it made a weird noise, used to shit them up proper. Note: if you try this on a road bike you are likely to end up on your arse.