Oh come on, are you sure you needed 10 minutes to stop a gash on your arm? I've had worse from a bad cat scratch and a bandaid did the job. Helmets are meant to take a hit, so unless your head was rattled too, it sounds like a standard day of tree work to me.

Honestly just go up and offer to show them how to do it. Most people at co-ops are scared to mess up their bike and just need someone to walk them through the first time. That's how I learned, some random dude showed me how to true a wheel while I was waiting.

Start wrapping plastic the wrong way and it's just inviting trouble down the line... I've noticed this same pattern with a lot of trades actually. Plumbers who don't bother with primer on PVC joints, electricians who stuff too many wires into a box, roofers skipping felt paper under shingles. It's like everyone's trying to save 10 minutes of work now and let the next guy deal with the fallout. The worst part is most homeowners never see this stuff behind walls or under floors until it's too late and mold or rot sets in. Gotta watch these guys like a hawk if you're not getting a good inspection done.