God how embarrassing, I buy a backpack, looks all fine, rather neutral colors and everything, but I look at a slogan printed small on it and it's tag, and realize it's a women's backpack when I got home. Worse of all, I didn't keep the receipt for it either.
Go ahead and laugh at my stupidity lol, I find it both embarrassing and humorous at the same time.
If it is schoolbag size, or it's one of those 20-litre daypacks, no harm done: go over the logo with permanent marker like TCO says, and no one will suspect a thing. If, however, you are talking about an 80-litre camping rucksack, they are designed differently for men and women as to where the support straps are positioned on your torso. If it's not right, take it back and get the right one.
I myself have nothing to bitch about at the moment.