Update: Barely after a month after this post, Yahoo! Mail fixed this issue. Amazing!
I filed a bug report on Yahoo! Mail’s infamous CSS Parser. A copy of the bug report can be seen here: HTML Sanitizer Breaks Mobile Responsive Email
If you’re tired of adding CSS hacks just to ensure your media queries don’t activate in Yahoo! Mail, feel free to give them a little nudge by upvoting this request or sharing this tweet :)