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 or 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. Experienced riders often point down with one arm to indicate something to avoid on the road as they start to shift their line. This action is then repeated down the line. Swerving and hard braking - not appreiciated in a bunch - is avoided by constant concentration and anticipation. This is part of being a good cyclist.
Something called "half-wheeling" is one of the cardinal sins of company riding. It's when the offending rider, typically on the outside, nudges 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, just say so and apologise and you will usually find that people won't get annoyed at your failure to come through.
Cyclists, being relaxed and understanding folk, NEVER ABUSE OR BERATE OTHER CYCLISTS OR EVENT HELPERS. The latter give up their time to make your day go as well as possible. The HHH crew includes juniors, charity volunteers and guys who drive a hundred miles to marshal for you.
You are advised NOT TO RESPOND BY WORD OR GESTURE to abusive or dangerous drivers, vehicle passengers, or bystanders. Instead: record events, identify witnesses, report offenders.