Most erotic rectal temperature position ?

I think there’s truly something special about being able to see her anus with the thermometer in it at the same time as her eyes.

On my back with legs pulled up means she's looking right in my eyes while she can see everything. In any position, it's a complete melding of trust, arousal, embarrassment... OMG too wonderful.

Seeing her face, her blush, at the same time as you can see her bottom and then slip it in, hold it, and wait - nothing to do but look at each other with her knowing her bottom has been violated by the thermometer, and by you - and you knowing she realizes you can see everything as well as her embarrassment.

Could any other position be more erotic?

—TYD

Lying across her lap on the sofa with my penis between her legs.

The most erotic position for checking a temperature is to lie face down on a woman's lap.