A lot of what you do as a lifeguard, just like as a teacher, is enforce rules. It's understood that you're the authority figure at the pool and that part of your job is to tell people not to run on the deck, or no diving in the shallow end. Most people are generally okay with this, even though the rules are sometimes a pain; they understand why the rules are there and are generally agreeable about following them.
The most notable exceptions are young people. Little kids, say under the age of 10, often don't follow the rules either because they don't know what they are, or because they forget. Older kids, say teenagers, often don't follow the rules for other reasons. They're pushing boundaries, they're showing off, they think it's entertaining to intentionally break a rule just to see what will happen, etc. Most of these incidents are handled quickly and easily with a simple verbal reminder, but occasionally you get a kid who's just out-and-out defiant.
A few days ago I was in the lifeguard chair at one of the pools where I work and there were a couple of middle-school aged boys playing near the rope that separates the shallow end from the deep end. One of the boys was actually sitting on the rope. I was pretty sure this boy knew very well that that wasn't allowed, but the rope is tempting for a lot of kids so I'm used to reminding them of the rule.
Me: Don't sit on the rope, please.
Boy: [Ignores me]
M: [Louder] I need you to stay off the rope, please.
B: [Ignores me]
M: [Blows whistle loudly] I NEED YOU TO STAY OFF THE ROPE.
(By this time the boy's mother, seated nearby, is also telling him to get off the rope.)
B: [Turns around as though he has only just now become aware of me] Oh, I thought he said "Stay off the ROAD."
At which point his friend snickered and I understood immediately the type of kid I was dealing with. I was hoping that the kid had had his fun and would move on to some other source of entertainment, but he seemed to enjoy this one. After the third similar exchange over the rope, I had the two boys get out of the pool and come over to the lifeguard stand for a heart-to-heart (they were reluctant, but they weren't getting out of it), and a few minutes later, during the 10-minute "no swimming" break, I went over and spoke briefly to the mom (with the two boys sitting there). She was very nice and apologetic, and I didn't expect any further problems from the two boys. As it turned out, they all left after another 10 minutes or so. (Maybe the boys decided that if they had to follow the rules at the pool they'd rather find something else to do.)
I meet so many young people, both as a lifeguard and as a teacher, who seem to know no way to interact with an authority figure other than to oppose them. The only way they know, or maybe just the way they're most comfortable with, is a very negative, rude, and occasionally hostile way of interacting. I'm not sure exactly why this is. Maybe that's how some kids interact with their parents, or maybe some learn it from TV and movies, where so many authority figures are portrayed as the bad guys, not someone to respect or try to work with, but someone to actively work against, or passively ignore or make fun of.
One tactic that I've found sometimes works to short-circuit this cycle of negative interaction is to try to have some kind of positive interaction with a teen (or pre-teen) as soon as possible. It doesn't have to be anything huge, and in fact I find that it's often better if it's something very small. Two that often work well with teens in a school setting are 1) a simple "How ya doing" when walking by one in the hallway, and 2) the old hold-the-door-for-the-next-person-behind-you-after-you've-already-walked-through-it technique. (This second one often prompts the teen to say "Thank you" which allows you to respond with "You're welcome" and suddenly you've actually had TWO positive interactions with a teen in the space of just a few seconds. Score!)
Notice that the purpose here is not just to create a more pleasant environment in which all of us can spend our day, although that is certainly a good thing all by itself. What I'm really hoping to do is get these young people to realize that there are other ways of interacting with authority figures than being surly and rude, and that there are in fact a lot of benefits *for them* if they can learn some of these ways.
For the kid at the pool, he might have discovered that he got to stay in the pool and have fun, rather than get called out in front of his mom and everyone else. For a kid in one of my classes, he might discover that math class still isn't as fun as hanging out with his friends but at least he can get along with the teacher.
For those who might say that these examples are pretty trivial social interactions, I have to agree, though that doesn't make them any less important. All of us need to learn to interact appropriately with authority figures, and for a kid whose instinct is to see all authority figures as the enemy, having a single positive interaction with one, no matter how small, can have a big impact. I know because I've seen it happen.
The fact is that I can't teach a kid math until we agree on which one of us is the teacher. And part of my job as the teacher, just like as the lifeguard, is to make and enforce certain rules, and if he's not gonna follow the rules, there are going to be consequences. But once he accepts the fact that I'm the one in charge, and that he can actually interact with me in a civil way EVEN THOUGH I'M AN AUTHORITY FIGURE, then all kinds of good things can follow.