I'm sure you've seen it before: at some point during Mass (usually after Communion), the priest may invite the congregation to extend a hand and join him in offering a blessing on a particular person (wedding anniversary, for example) or a group of people (retreatants, people going on a mission trip, etc). So the entire congregation raises their right hands with the palm extended and facing downward, as if to join the priest in offering said blessing. I never join in on such blessings, first because I believe that it is only the Priest who can give a blessing, but also because the first thing that comes to mind when this happens--and I mean to offend NO ONE--is "Heil Hitler".
Is there any particular document or teaching relative to these blessings? I'm not trying to change the way my (or any other) parish does things, I'm just curious to know your thoughts.