What do you think? How do you know when to offer help and is the idea of stealing someone's man card as big of a deal as I think it is?

Same like you : the whole "let me step in and show you how it's done" feels a bit wrong". I have tried to do that few times and seen people taking it in a negative way, so it's best to mind our own business, unless someone asks for help.

The only time I would step in without anyone asking is when someone is in need of medical urgency, where he/she is not even in a situation to ask. Otherwise, now a days, people react very harshly.