I've certainly noticed that some days seem worse than others for people not paying attention to their surroundings and either stopping in front of me, cutting me off. When it seems to increase, it occurs everywhere, be it in the grocery store or while driving down the highway. Some times this can last for a few days at a time.
I have but three ways of viewing this:
1. I am more sensitive on those days and notice things more (therefore, the change is internal, not external)
2. Even randomness can appear like a pattern. Shuffle a deck of cards as best as you can, and there's as much chance the aces will be together are them being well distributed (therefore, this would simply be a coincidence)
3. There is a plot to make my life difficult
I am leaning toward 1 and 2, since my life is already difficult and having people slow me down or inconvenience me really isn't a big deal in the bigger scheme of things. If somebody wanted to make my life more difficult, it would make more sense to vector through people close to me, who can apply constant stress, not 15 minutes in a grocery store. Putting sugar in my gas tank would be more effective.
However, even if this were becoming a constant pattern, I would just use it as an opportunity to develop better navigation strategies. It is too easy to worry about who might be behind such things or why I have been targeted.
As things get stranger in our world, we might see more and more people getting distracted and not paying attention. Consider them obstacles to practice navigating around.
As well, with respect to Laura's suggestion, you will probably gain some interesting insight reading the Cognitive Science board. It's amazing how our mind can perceive all sorts of things that we swear are a certain way, when in fact, they simply aren't. A good example is people seeing certain numbers constantly repeating in their lives. Our mind has evolved to detect certain patterns and to ignore anything that doesn't seem relevant. When we combine this ability with certain programs we might have running or that might get triggered, it's amazing the patterns we see when none exist.