During a sportive you may find yourself riding in a large group, a small group, or on your own. When riding with others, the principal rules are not to ride in a way that ENDANGERS your companions and not to ride in a way that ANNOYS them.
Don't ride tight on someone's back wheel ("wheel-sucking"). Ride instead slightly to the side to give you a get-out if someone brakes. It also gives you a view of the road ahead. If you see or hear a significant danger, call out, as in: 'Hole!' or 'Car up' i.e., up ahead, or 'Car back', i.e., it's coming from the rear. Older club cyclists have quite a repertoire, most of which is self-explanatory. Often, experienced riders just start to shift their line while pointing down with one arm, this action then being repeated by those following. Swerving and hard braking is usually due to a lack of concentration and anticipation. Not appreciated in the bunch.
Something called "half-wheeling" is one of the cardinal sins of company riding. It's when the offending rider, typically on the outside, pushes ahead of their companion by just half a wheel.
"Sitting on" and "not doing your turn" is not well thought of either. Sportives are not races but even so, there's a common interest in getting to the finish. If you are genuinely hanging on, say so and apologise and you will usually find that people won't resent you for being permanently at the back.
Cyclists are an enlightened and altogether higher form of life. Cyclists NEVER abuse other cyclists or event helpers who as far as the HHH is concerned include a few youngsters who are support team veterans of not only the HHH but also other sportives, and give up their time to make your day go well.
You are advised not to respond by word or gesture to abusive or dangerous drivers or vehicle passengers. Record details, get witnesses, and report.