There is always someone....

Around here (SoCal S OC and N San Diego) it is better to tell them to knock it off. Or stop and let them go. There are too many variables and knuckleheads of vastly different abilities. Beginners on pro bikes, to the electric bikes, to some surf camp kid on a MTB thinking he can mix in with the "real riders". There are plenty of group rides that welcome you and plenty of solo riders you can get to know, then ride with. But jumping in with strangers, esp those without their hands on the bars is increasing risk considerably - esp in higher speeds.