Some 1.6 billion of them are yours, courtesy of Archive.org.
This is an archive of Reddit comments from October of 2007 until May of 2015 (complete month). This reflects 14 months of work and a lot of API calls. This dataset includes nearly every publicly available Reddit comment. Approximately 350,000 comments out of ~1.65 billion were unavailable due to Reddit API issues.
You'll be needing about 5Gb, just for the compressed dataset.