Back twenty years ago when I first started seeing "SMH" it was "So. Much. Hate."
As in "I really dislike that."
As in "So, everybody unanimously said they want sheet cake for office birthdays and management decided to double down on the day old donuts again anyway? So Much Hate."
I think it was the original meaning when it was brand new and still very niche.
Part of me wonders if it made it onto one of those "Parents! Know these abbreviations!" memes where they purposely list the acronyms incorrectly (LOL--Lots of Love) and then got more popular that way.
Edit: decided to look into it further and found this page with an interesting tidbit from 2013 regarding dilution of Google search results:
While finding out what SMH stands for took about 10 seconds, it's what I noticed along the way that really struck me - Google's search results for SMH. I always like to examine interesting first page search results whenever I run across them so we can all better understand the direction search is headed. Before I dive into the details, take a look at the screenshot (click to enlarge):
See how these results differ from regular old Google search results?
Merrill Lynch Semiconductors HOLDRS ETF stock quote results at the top, complete with buttons to change the date range as well as links to details on SMH at Google Finance, Yahoo! Finance and MSN Money.
The "Knowledge Graph" area to right has image (logo) and text links to the Google+ page for the Sydney Morning Herald. Just below is a photo, excerpt and link to Sydney Morning Herald's most recent Google+ post.
Also in the knowledge graph is "place" preview info for Sarasota Memorial Hospital (another "SMH"). As with most things in the knowledge graph, however, this just links you to search results for "sarasota memorial hospital", whose website domain is smh.com
Back in the organic results, we see both the Sydney Morning Herald and Sarasota Memorial Hospital, along with related twitter accounts, Urban Dictionary definitions for SMH, etc. Also smh.org - South Mental Health. Lastly there's an app in the itunes store for the Sydney Morning Herald