Sherry and I have promised - we have sworn - that we won't squabble on this trip.
"I won't needle you if you won't snap at me," I told her on the phone the other day.
"I only snap at you when you needle me," she snapped, and I decided to let that pass in the interest of keeping peace for a week in a Lilliputian shipboard cabin.
There are good points and bad points that I can see in us having a tiny private balcony outside our floor-to-ceiling French doors. It will be a good place to cool off if the discussion of who sleeps in the bed nearest the view gets heated. But if one of us tosses the other one overboard from there, everybody will guess who did it.
We're cruising up the Rhine River from Switzerland, through France and Germany, to the Netherlands, otherwise known as Holland.
Before that, we're spending about 12 hours on an airplane seated next to each other and we're sharing a ride to the airport.
I know. It doesn't sound good. But it's doable, we think, if we just remember to be nice to each other.
Why is that so hard? We've been friends for more than 15 years. In a lot of ways, we're like sisters. So why do we squabble?
Do you have a sister?
We enjoy each other's company but we tend to get crossways when confined to small spaces. Like a car. Or a hotel room. Or a small Third World country.
Room temperature is a problem. She believes it should be low enough so the ice in your glass never melts. I prefer not to sleep in a sweat suit, three pair of socks and a ski mask.
We didn't speak to each other on an airplane all the way home from Savannah after a little snit over an autographed copy of Midnight in the Garden of Good and Evil.
She once threatened to put me out of the car on a twisty mountain road unless I stopped shrieking and clutching the dashboard on every hairpin curve. I once threatened to put her in a column after she threw a tantrum in a drugstore because she couldn't find an eyelash curler anywhere in Taos, N.M.
She's the one who gave me the leopard-print handbag with the rhinestone buckle for Christmas that year.
"You're going to just hate this!" she said, when she handed it over.
And she was right. I do hate it. But what are old friends for if not to figure out what you dislike the most and give it to you for Christmas.
Still, I love it. And she knew I would.
Some handbags, like some men, are absolutely adorable and totally dysfunctional at the same time.
We rarely disagree about handbags or men.
I once walked through her house and counted five television sets: living room, bedroom, kitchen, exercise room and, oh yes, one on the deck in case she needed to catch a gadget infomercial in the hot tub.
The TV in the living room is about the size of my refrigerator, and - who knows? - it might dispense ice cubes.
She's the one who tried, literally, to throw me to an alligator while we were in Savannah. Our tour guide, Martha, had a penchant for gator-calling, and she drove up to a little bitty pond and started her act.
"Come heay-ah, lil alligatah," screeched Martha in her Georgia peach martini drawl, and something began to surface: something with a big head and wide jaws. Something 5 or 6 feet long.
It came close to the bank and regarded us with an evil grin.
"Oooh! Can you see from ovah they-ah? Get out and take its picture!" Sherry whispered. She thought that was funny. Funny is not hobbling back to Texas on nubs because your feet became alligator hors d'oeuvres.
She's fretting that she won't be able to Skype on her iPad on the cruise. I don't care that my smartphone is too old to support international calls.
"Don't you think you could do without Skype for a week on a cruise when there are castles to look at?" I needled.
"You worry about your gadgets and I'll worry about mine," she snapped.
Oh yeah. This is gonna be fun.
By the time you read this we'll be touring the ruins of a German castle. Or watching someone carve a cuckoo clock in the Black Forest. Or drinking mulled wine at the Christmas markets.
Or one of us will be swimming up the Rhine, trying to catch up to the boat.
DONNA FIELDER can be reached at 940-566-6885. Her e-mail address is firstname.lastname@example.org.