I am always careful to prioritize my comments during code review so I don't come off like that too often.

I'll say things like, "I would have done that like this because of this reason, but as long as it works"

or "This needs to change right now because it's a security hole"

or "We should find a more efficient way to do this, because as the data fills up, the users will start to notice it"

I am definitely harder on new people, and people who ask me for help when they should have been able to figure it out on their own.