Terms of Endearment
In the Threesome Drabbleverse
"After all this time and all you've gone through, you still don't use his first name," Skinner mused.
"She does have a pet name for me though"
"Do not," Scully was slightly red-faced, probably about being accused of such sentimentality.
Mulder replied, totally deadpanned, "Sure you do. You call me Dammit Mulder all the time."