hahahaa... well, technically, (sort of like your scenario) my last name's first initial is "t" so yes, it's monica t.
however, one of my good pals always calls me moni-cat and so there's a bit of that too. maybe it's both.
i started using the "just" one year when i got a little fed up with bankers (looking at you rach : ) saying to me, ok, so when will you have your husband (or once, my father) come in to sign the papers on your house purchase/business loan/investment account and i would have to repeatedly (or so it seemed) tell them ,
"oh, no, it's only me. it's just monica t."...
that was also a year that i was on the road a lot for business and i was constantly eating alone in restaurants as well. so i guess i embraced the whole "it's just me" thing.
now, i just feel like just_monicat is a well worn pair of jeans that i enjoy hanging out in : )
and thanks for asking. when i read about your explanation on the other thread i chuckled about my assumption of the moniker (like everyone else).