For instance, one of my classmates mentioned in her joke that she had vaginal bacteriosis (yeah, we can get pretty personal in class), and now it seems like I'm seeing articles everyone online and in magazines about this condition.
Another classmate wrote a joke about how the word, "thus" bothered him. I've never really given "thus" much thought; I was neutral about the word, but ever since I heard the joke, it seems as if I'm seeing it everywhere. And now it feels like it jumps out from the page to taunt me.
These examples show the frequency illusion at work where once you learn something it appears like it pops up everywhere. Be careful what you pay attention to, folks!