For example, it's the first day at your new job and one of your colleagues is supposed to introduce you to the new working place. The person rants about everything in high speed without paying attention to whether or not you understand what he's saying.
closed as too broad by Robusto, Rory Alsop, user66974, Kit Z. Fox♦ May 23 '14 at 11:39
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Blatherer or Blatherskite (thanks to Hellion for the latter variant). There are many rich expressions and words for people who talk too much, which I gather is part of your complaint because you said "rants about everything", but you also added "at high speed without paying attention to ... you ...".
So I'd say "blatherer" is a good compromise. Motormouth, already mentioned above, captures the rapid and excessive part, but doesn't convey the lack of empathy generally. I think it is fair to say that blather usually implies long-winded, self-absorbed nonsense.
You could combine them and say "For my introduction, the motormouth just blathered on and on."
An egocentric, unempathetic boor.
I think you can call him motormouthed, maybe blabbermouthed.
Consider unconcerned and blasé.
blasé: having or showing a lack of excitement or interest in something because it is very familiar
A closed mind with an open mouth.