Code:
on *:TEXT:*hello*:#:{
  INSERT CHECK HERE
  msg $chan hello
}


Replace INSERT CHECK HERE with any of these:

if ($nick == somenick) { return }
if (something isin $nick) { return }
if ($wildsite == *!*@host.com) { return }
if (something isin $wildsite) { return }

Note that you can avoid using return with all of those by doing != instead. I'll show one example and you should be able to convert the rest yourself.
Code:
if ($nick != somenick) {
  msg $chan hello
}


Note that this required putting {}'s around your message instead of just inserting the line above your message.

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