I think this looks pretty simple but also well done and nice. Not a fan of the plan style because its just a quote in white text slapped onto the man style, but I do think the other ones fit into the game just fine.
Also I'd pass all the stuff listed in the comment below a pass because it fits the game's style which is more than just a military shooter set in the 60s. I'd point more toward stuff like the recent christmas and halloween hats that look like they fit in roblox more than any kind of shooter.

Like the three hats stacked on each other, a ripped lab coat with pecs sticking out, suits, chaps, pajamas, flip flops or basically any lack of military equipment?

I agree with Limecatcher and למשח ינסחמ. This wouldn't make sense to wear on a battlefield in the middle of New Mexico

Such a good cosmetic, but it confuses my brain so much

The Fan style is probably my favorite out of all three. Keep up the good work.

I don't get the hate. I think it's a cool and well designed cosmetic and I like the band references.

I can understand you disliking the Plan style, as yes, it's a silly phrase (that Engineer actually says in game), but the Fan style is literally a parody of two rock bands. What's silly in that?

Despite that, I don't see how it doesn't fit the game. It's a t-shirt, these things existed for decades before the game takes place. If you think that's pushing I'm genuinelly surprised you've never seen what people wore in the past.

As a member of the Beatles I’m quite fond of this cosmetic

למשח ינסחמ makes my points clearer

looks too casual for the class its on, just my opinion but this'd fit better on someone like Scout or Demo than Engie.

lame, kinda unattractive and doesnt fit the game's, nor the engineers, overall style
this is just a buncha lame puns on screen printed tshirts, no thank you

genuinely just the look of engineer in a tshirt would already be better than all these silly little prints, and even that's pushing it

What makes it bad for an in-game item?

great for GMods and SFMs, not so much for an in-game item. neat but Pass.