Haha. I know I keep posting but I keep finding more bag options for you! I ran into a similar problem with needing a less feminine but still inconspicuous dog bag and these are all the bag options I found.
Airline Approved Unisex Town Pet Carrier
I still think this bag looks feminine, though? But it is listed as unisex.
Sherpa Tote Around Town Carrier - Black
This one looks like a pet bag ... but a little less so?