Adversaeschna brevistyla (Blue-spotted Hawker)IUCN Status: Least Concern.
These are big, chunky, aggressive dragonflies. In fact if you do any googling you'll see people saying they are the biggest they've seen. Like most dragonflies, they are also very territorial.
Being territorial, coupled with high populations in summer, and a tendency to wander, means that interactions are occurring all the time. They have excellent eye sight, and if they spot competition flying too close they'll be on the wing in an instant, seeing it off. Altercations are frequent, and surprisingly noisy.
If you observe dragonflies, you'll often see males clash so violently that they plummet out of the sky into the undergrowth. I've seen fighting males plunge into the water. It's a very testing way to spend their last days in such a beautiful new form, having spent most of their lives as aquatic nympths (also super aggressive).