OP: You've already been given good advice, namely, don't talk about running.
But, nobody has really answered your question yet, namely, why do people get angry about this. Also, I do think that people get more angry about running than other sports/games, such as bowling.
I think people don't like it for a few reasons. IMO, the two biggest reasons are the following:
1. Many people have only encountered running as a form of punishment. E.g. in other sports, (just) running is used to punish people for making mistakes, or running is used to punish a losing side during a scrimmage. In gym class/PE, running is a common punishment. In HS, gym teachers can't make students 'drop and do 20,' since so few students can do that (and yes, that is sad), so running it is!
2. Somewhat related to point 1, people feel - whether justified or not - that runners perceive themselves to be better than others because they are electing to do what others do only because they have to. Now, I've met some very self important runners, but of course I'm met humble runners as well. But, the image is definitely that runners are some sort of haughty spartan, looking down at all plebs who lack discipline.
(2b. Some people also think that running hard is actually bad for you, and that therefore in their mind, you are not only a self-important prick, but you are also a wrongheaded self-important prick.)
Less important:
3. People view it as selfish. Doing things around the house and/or for your kids is seen as normal. Running is seen as solitary and selfish. (Again, this relates to points 1 and 2 above, since most people do take time for themselves on a daily, it's just that running is seen as more selfish)
4. Some people are uncomfortable not by your running, but by your dedication to being a good runner. These same people might celebrate somebody who is out of shape and then does a couch-to-5k program (and yes, that person should be celebrated). But, some folks are so out of touch with the concept of pursuing excellence for personal reasons that it makes them uncomfortable. They assume that you look down on them, when that may or may not be the case.
Finally, I also don't like bowling. But, I would think it's cool if a coworker was super into it - why not?
But yeah, don't talk about running.