You know you're DID when...
You enter the shop as a competant adult determined to follow your list and make only practical purchases, and then get home and realise you've spent the week's grocery money on pinwheels, Barbie dolls, Lip Smackers, candies and plushie animals because your child alters took over.
When your friend sends you 3 or 4 cards for the same event, each for a different You

When your SO gets used to giving you sexy lingerie and Legos in the same package.

When friends call and think they mis-dialed because they don't recognise the voice on the other line. And when complete strangers call and insist they actually are your friends!
When the person on the other line asks if your mommy is home since the child alts got the phone first.
When a friend tells you you simultaneously raved about your new fad diet plan while eating a pint of Haagen-Daaz in front of them.