it is funny because the "stress-relieving" box of tea has very visibly had frustrations taken out on it.

it is also funny because "stress-relief" should have been hyphenated. as it is currently written, the term "stress relief" means "emphasize reprieve." since the the alleged reprieve has indeed been emphasized (by way of the aforementioned box-mangling), the title – "One of my roommate’s tea boxes stands out to me… I’m not sure why" – is making a second joke.

finally, it is also funny because there is an asterisk next to "soothing serenity blend." if you look at the back of the box, the caveat will probably say something like "The term 'soothing serenity' is being used to mean 'causing of explosive diarrhea that has been classified by the Geneva Convention as a weapon of mass destruction."

(it may not actually say that, but it would be very funny if it did.)