[Crowley caught on to how sensitive Aziraphale's scalp is long ago, long before they had the relationship they do now. Now that he has explicit (and frequently reconfirmed) permission to do so he takes shameless advantage of his knowledge. Turning Aziraphale to putty has been one of Crowley's favorite hobbies since Bethlehem. Though doing it in this form has certain advantages that Aziraphale's cat form doesn't offer...]

Can't imagine where you got that idea from.

[He sounds almost gleeful, because this is absolutely his favorite way to spend time. Aziraphale his more or less melting back against him, and Crowley carefully rubs his fingers in little circles next to Aziraphale's ears, then continues them along his hairline.]

Though given that we're in a bathtub of soapy water, I'd say I'm playing entirely clean.