Just to annoy the stern Hebrew School teacher, who thought it sacrilege, occasionally Joe would inquire, “Barukh who?” and Herby would reply emphatically, “Barukh, schmo!” (True story.)
When a leader begins a berakhah, after s/he says, “Barukh Attah Adonai,” those who are not reading collectively respond in a sort of reaffirmation, “Barukh Hu, uvarukh Shemo,” which translates as, “Blessed be He and blessed be His Name.”
Some say only “Barukh Shemo,” which may have begun with congregants eliding the words together.
Some consider whether saying it in any certain blessing might be an interruption, and may omit saying it out of respect, or for other reasons.
Then, of course, when the reader ends the berakhah, generally we say “Amen,” “so be it.”