What's Fjallraven?
One of the main male fashion options - in fact female too - is the cheapo t-shirt with writing on, the slogan T-shirt is merely a large subset of this. I think they are seen as a pretty safe option so they churn them out by the ton.
There are so many there are even different categories; the "witty" ones that say something like "if you can read this you're too close"; the ones based on some kind of made up or defunct blue-collar sounding US company eg "Auto-repair and parts shop" which often have random bits of meaningless info stuck on them, plus they tend to rep the nowwheresville town where Earl purportedly opened his garage; thirdly you've got the band ones which I think you are only allowed to wear if you've never actually heard of The Ramones or Metallica or whoever it is - if you had heard of them then you would be buying their t-shirt at a gig not at Top Shop.
The above are such boring and lazy clothes, especially when they just stick the writing on an otherwise bog-standard t-shirt. I mean when I was little I liked band tees but when it hit me that they just lazily iron the name on to a super low-quality teeshirt from the town centre market I gave up. Why is so much merch so uninspiring?
Anyway, with what I said above about men being bullied out of wearing almost all clothes, these types of slogan T-shirts are ubiquitous, they are the Marvel Films of clothing in other words - lowest common denominator bad taste bollocks for morons who have never and will never grow up.