The expression may refer to either of two types of luggage:
1) The more proper use of the term, referring to any number of large wallets or small shoulder bags, distinguishable from a woman's bag only by subtleties such as rectangular shape or plain decoration. A cultural equivalent to the fanny pack craze of a generation ago, these are likewise gaining in popularity despite their perceived tackiness. (Whether this is due to their relative practicality, European style, or to the influence of metrosexual culture, is open to debate.)
2) Larger, more masculine carry-alls such as the satchel, shoulder bag, or messenger bag, worn as an alternative to the backpack. Less scornfully viewed than those under the first definition, these have been lately popularized by such fictional characters as Jack Bauer, Indiana Jones, or Chewbacca, and are actively displacing hard-sided briefcases in some quarters. Use of the term in this context is less justified, and indicative of both bitterness and extreme homophobia.
2) "It's not a man purse, it's a shoulder bag.....asshole."