The one that really bugged me was in the last Avengers movie, Civil War. A couple of our heroes are being shot at with what are clearly fully automatic rifles. One of them (I think it was Captain America) says something like "those are AR-15 rifles they're shooting at us." The line was completely unnecessary and had nothing to do with the plot or anything else. It just felt like blatant propaganda. "Let's point out that the terrorists use AR-15s and that they're fully automatic. Yeah!"
On a related note, I actually know how to pick locks. I'm not great at it, but I can open most basic door locks. Seeing what passes for lockpicking in movies just annoys me to no end. And how does every person in movies know how to hotwire like any car? Okay, I better stop now.