The other day, I had the rare joy of teaching some friends how to use Twitter. I used to be able to fill an entire day's training session – and entire room – with my thoughts on how to use Twitter for brands. Don't laugh. In a pre-Facebook world there was a lot to discuss.

But I have to confess, I felt a bit fraudulent helping some new folk get into it when I've been a little off Twitter myself in recent years. I used to be on Twitter hourly. Now? Perhaps weekly. I'm not sure exactly why. I know I'm part of a general trend towards user decline on Twitter, but I started to worry my Twitter advice is out of touch.

Take the hashtag for example. My friends asked the usual "Everyone's using them – should we use them? How should we use them?" My rule for Twitter newbies has always been a bit like Mr Miyagi to The Karate Kid – if you're asking me how to use a hashtag, you're not ready to use a hashtag.

"Why? What will happen if we use the wrong hashtag?" my students always ask. Well, of course, nothing. But there's a subtle art to it. Like knowing the difference between what makes a great headline or is just icky click bait. The hashtag used badly, reeks of desperation to me. And cool people don't follow desperate people online.

But now I'm a geriatric tweeter in internet years, I wondered if I was being desperately uncool. Like people who still start emails "Dear Darika". Hashtags have gone way beyond Twitter now. The protocol, originally created to help people find similar content and track conversation trends within Twitter, is now used on Tumblr, Instagram, and even rival Facebook. People say hashtags in spoken conversations: '#ItsTrue', '#ItsIronic'.

But if you're going to use hashtags hoping to be found or hoping your content finds its way to a wider audience, you're going to have to be smart about what's actually useful. For example, I frequently see the hashtag '#business'. Nobody goes "Hmm, I'm going to go online and read about some business now". It reminds me of the film Romy and Michele's High School Reunion (spoiler alert), where they decide to dress up as businesswomen, head into a diner, and try to order a businesswoman's lunch special – receiving a pitiful expression from the waitress for their naivety.

It's the same expression I gave recently when I walked past a giant Iceland billboard emblazoned with #PowerOfFrozen. I mean, what the hell? What kind of hashtag is that? I checked on Twitter to reassure myself it would never catch on. And here's the thing. It was being used. Sometimes by people to deride the campaign but others were using it to tag their happier thoughts about Iceland too.

It's hard to explain what's so irritating to me about the Iceland hashtag. Maybe I still believe that successful campaigns and brands should wait to be lovingly bestowed with a hashtag from their fans. Or maybe I'm so old school I don't think any ad campaign needs its own hashtag. The best hashtags become movements – a shared conversation between thousands of strangers on the same topic. When I think hashtag I think #ArabSpring. I think #BringBackOurGirls. I think of shared moments in pop culture like #RebeccaBlack. I never think "Let's talk about advertising frozen goods".

And maybe that's what's really annoying me about hashtag abuse. Most of the population still don't know what these hashtags promoted in ads really mean. And I'm not sure all of them have developed their wax on, wax off skills to use them. Hashtags were something developed by the users of Twitter. The digital natives. The reason I told people they could use a hashtag once they didn't need to ask me about them was because I wanted them to genuinely log some hours on the platform first. Understand the etiquette. Become part of a community. Certainly before they started doing any brand promotion.

I fell in love with platforms like Twitter when I was a digital native within them. And that's how I thought of ways that brands could positively contribute to the environment. But could the growing presence of brand tourists exploiting the natural landscape be the very thing that's made me and others fall out of love with Twitter?

Facebook seems to be heeding the warning signs. As marketers, we're getting frustrated at Facebook constantly redrawing the rules for what brands can and can't do to promote themselves on the platform. But by pushing brands into clearly defined advertising slots, they are protecting their communities. Maybe 'the youth' are abandoning Facebook for being uncool. But isn't being around for a long time really what's cool? Just ask The Rolling Stones.