Some artists (Voidless comes to mind) like drawing him without a shirt because quite frankly it looks really cool, especially if you keep the hoodie on. Making him topless and posing him as if the image is supposed to be lewd, though? Yeah, I'll never understand that.
My boyfriend found this cuddle pillow case on Amazon with Sans half dressed with his thumb in his shorts looking into the fourth wall and blushing furiously. The blushing thing is quite frankly adorable but... really folks? My boyfriend can't get over how I've admitted I'm in love with the character and I DO think he's kinda sexy (Because of WHO he is, not WHAT, urgh) and yet I find the pillow creepy as all getout.