Dolphins don't always want to be around people. There are many reasons for this, and those reasons are just as many and varied as when one person doesn't care to be in the company of another person. Regardless of the reasons, dolphins can and do give very clear indicators when they want to be left alone, body language that says, "DO NOT DISTURB".
As a guest in the dolphin's domain, it is your responsibility to be aware of all the signals, not just for the nice ones, and act accordingly.
Misunderstandings that humans have with dolphins occur when the human has a personal agenda. An agenda that focuses on their own wants and needs and ignores those of the dolphins. A relentless pursuit to be with the dolphins is stressful for the dolphins, especially the elders and adults, who are more suspicious, and have experienced the unpleasant side of being around humans (being harassed, chased, shot at, beaten, run over by boats). The elders are very protective and will display negative behavior that could result in someone being hurt if an overenthusiastic swimmer pushes too far.
If you notice any of the dolphin warning behaviors listed below, leave the dolphins alone. They are saying they don't want your company. If you are not sure whether or not you are seeing negative behavior, give them the benefit of the doubt. Maybe they had a bad night's fishing, had to travel far to hunt and are extra tired, or were harassed at some point. The dolphins are going to be around a long time, so if you experience any of the warning behaviors, go with the flow and go away or get out of the water. There will be other swims.
Humans who don't pay attention to the obvious needs and signals of the pod usually elicit the warning behaviors listed below. The dolphins are forced to act in more aggressive ways to get their message across. They are teaching us how to be with them. We need to not be so focused on our desire to swim with them and respect them in every way possible.
These are specific dolphin warning behaviors:
Pod formation: When the pod is swimming in a tight formation, it is usually an indication that they feel threatened in some way. Many times they will surface to breathe, away from any swimmers, and go right back down to the bottom still bunched together. This is a very passive warning to leave them alone. Give them plenty of space, don't approach the pod, and especially, don't dive down when they are submerged.
Circling away: If you are swimming toward the back of the pod and a dolphin in the rear swims up next to you and circles you away from the pod, it's an indication that the dolphins do not want you near. The dolphin will swim close to you in a certain direction, forcing you to move that way or bump into it. When the dolphin has circled you all the way around and you are facing the original direction, it will speed up after the pod and you will be let in the dust. Stay there. Another clue that you're no longer wanted is if the pod surfaces ahead of you or swims faster when you come near.
Vocal Warning: This is not the pleasant whistling sound you usually hear, but more discordant "chit, chit, chit" kinds of sounds, as if you are being scolded. And if you did something inappropriate, chances are you probably are being scolded.
Tail slapping: Tail slapping can be a game when the dolphins are playful and relaxed. However, if a dolphin is tail slapping near you, and no other dolphins are playing, the pod is resting and not interested in interaction; most likely you are being warned to "back off."
Spinning in close proximity: Spinning can be another warning to "back off" if, as with tail slapping, no other dolphins are playing or interacting.
Tail Thrashing: This is a very clear signal for a human to "get away." Unlike the tail slapping described above, this behavior takes place below the surface. The dolphin will wag its tail from side to side or up and down in a very fast and intense motion. If you are close to the dolphin when this happens, the water will surge around you because of the intensity of the thrashing. Move away immediately; the dolphin is telling you to do so in no uncertain terms.
Humping up: The dolphin humps its back up and its body takes on an "S" shaped curve. This is an aggressive warning, and if you are sensitive to energy, you are getting really "bad vibes" from this dolphin. Swim away and leave it alone. The dolphin may trail you for a while to make sure you get it, so just keep going.
Jaw snapping: This is a very aggressive move on the part of the dolphin. If a dolphin snaps his jaws at you, leave immediately. This is a sign he's very agitated.
Charging: If a dolphin charges at you, get out of the water. If a dolphin charges at you, get out of the water. That's most likely what it's telling you to do. If you can't tell the difference between an aggressive charge and a game, don't take a chance, get away or get out.