Wtf is childish about a rucksack? As long as you have a proper manly rucksack its all good, not a cheap Nike or adidas school bag!
I feel naked without my rucksack I have used one for so long.
Oh... and a man bag is obviously a very gay item no matter how you dress it or how manly you think it is...
Either you man up and get a rucksack or a briefcase or you start batting for the other team and buy a man bag, start exfoliating and before long you will surely be booking your first peticure/manicure and then you will be thinking about elton john rubbing baby lotion on your silky smooth abs of steeeeel....