I have a standing date on Wednesdays with a man who makes my knees weak. He works me to exhaustion, until my arms and legs tremble and then, as I collapse onto the floor, he says: "Come on, only 30 seconds more. Squat jumps!"

I admire and loathe and sometimes fear my personal trainer. In the heady cocktail of gym endorphins, I even understand why some clients fall for theirs. It's probably Stockholm Syndrome. You feel a rush of affection out of sheer gratitude that you're still alive.

But you should never date your personal trainer. I can't believe this has to be spelt out but I have had to in conversations with friends. It all started when one of them was talking about the difficulty of meeting prospective romantic partners in one's 30s and 40s.

Another suggested she join a popular fitness chain brand. He named a particular outlet as "hook-up central". "The trainers are cute," he added.

Joining a gym to date the trainers? This is a betrayal of trust and a ridiculous waste of money. This is mistaking someone's professional interest in your health and fitness for a different kind of intimacy.

I agree that it is hard to find, make and sustain personal connections especially in one's 30s and 40s. Friendships and other relationships require an investment of time, a slow give and take of information and trust that Hollywood movies and Young Adult fantasy novels would have us believe can develop overnight in a flash of hormones.

It doesn't. And it becomes harder to develop that sort of intimacy when ordinary person-to-person interaction is hard to schedule.

Communications are increasingly technological and confined to the screen of a smartphone, whether to follow up at work or set up a dinner date. Long working hours and other demands make it difficult to spend face-to-face time with people who work and live outside your own office building or home.

It is easy then to invest great meaning in ordinary everyday interactions with, say, the barista at the local coffee shop or perhaps the counter staff who greet you at the gym.

I'm not saying friendships and courtships have not developed through such interactions. I'm saying it has become easier to mistake ordinary courtesy from someone doing his or her job for a signal that the person feels something for you beyond the simple respect anyone should feel for another human being.

I spoke to friends and colleagues to compile a list of the worst misunderstandings they have encountered - or created.

If the girl at the fast-food drive-through counter offers extra napkins, extra sauce and an extra-big smile, just smile back, wave and drive on. Do not ask for her number. She's only following company policy.

The barista who gives you free refills and remembers your name is probably doing the same. Don't develop a crush on her even if she gives you free cookies. Check the time you receive the treat. If it's 6pm or later, she's probably just trying to avoid wasting food.

Apply the drive-through principle at restaurants and all service personnel at eating establishments, even those where the chefs are dishy.

Never ask your doctor out. Even if you change GPs beforehand, they probably know far too much about you for it to be comfortable.

Definitely do not ask to date your psychiatrist.

Do not fall for your lawyer (apparently this happens).

Do not date your teacher unless you have graduated, are a legal adult and are gainfully employed.

Do not date your student, ditto, unless he or she has graduated, is a legal adult and is gainfully employed.

No interns. No interns. Former United States President Bill Clinton, need I say more?

With people encountered in their professional capacity, there is a power imbalance. One party knows too much about the other, in the case of a doctor or lawyer.

One party wants to avoid offending the other, in the case of service staff, and should not be put in a tough position.

So if considering dating a colleague, at all costs, avoid entanglements with bosses or subordinates - and probably anyone from the IT department. (It is possible to kill an inbox with too many funny cat videos.)

There are different levels of intimacy and connection. All should be cherished. Not all have to be sexual or romantic.

Especially at the gym. If there's anyone you should be falling in love with at the gym, it is not your trainer or even any of the other regulars.

It is yourself and your increased physical capabilities. Nothing else.