Hashtags first gained popularity on Twitter. They were a way to tag your post with some meta-data to make it easier to find in the the glut of information on the web. So if you tweeted something about the royal baby you can use the hashtag #royalbaby. That way if people are searching the wide world of the interwebs for information, you can narrow it down a bit with a hashtag.
Then, a newish use of the hashtag emerged. You could use the hashtag to make a funny comment, or wry aside about what you were posting. So if I tweet a link to this Buzzfeed article about how I am addicted to Diet Coke I might label it with the hashtag #dietcoke to provide some meta-data info, and an additional hashtag of #sorrymom to make a little joke about how my mom is worried about my Diet Coke addiction and is sure that I will soon have stomach cancer.
But then you got stupid. And you started to abuse the hashtag. And it got ridiculous and inane and obnoxious. You see, a well placed funny hashtag can really give a tweet or an instagram a funny twist that you might not have seen otherwise. But when you just write 17 other comments after your original caption but make them into hashtags you just seem greedy and irresponsible. For example, this is what I see on Instagram all the time, using a photo of my friends Christian, Ken and Patrick chopping down 1 million trees at Patrick's new house, Sequoia Shadows.
And while we are on the subject, here's another way that you can use the hashtag wrong:
Ah, baby Hashtag. You are going to have a long interresting life. #becauseyournameishashtag #andpeoplearegoingtothinkthatyoucray #orattheveryleastthatyourmomiscray #amirite?