That's my thing

Saturday at our friends' apartment swimming pool:

While Eva hit the restroom, Isobel and I tested the hot tub.
I paused at about knee depth -- "Wow! That's hot." -- and looked over at Isobel. She was already up to her neck.

"Isn't it hot?"
"Not really. This is my thing. When I shower, I turn it on this hot. I like hot water. It's just my thing."

About 5 minutes later, Eva was dipping her toes in the water and Isobel was headed back to the pool. A couple of minutes after that, Eva had eased in up to her shins.

"I have to let the water get warm and then get in a little bit more. This is just how I am. I don't know, it's just how I am. Is this how Isobel is?"
"No. Isobel got right in up to her neck and said, 'This is my thing.' "
"Hmm. That's how she is. But this is how I am."