Trevor

Scully:  Hmm. [long pause] Spontaneous human combustion. Mulder:  [grinning] Scully...! Scully:  Well, isn't that where you're going with this? Mulder:  Dear Diary:  Today my heart leapt when Agent Scully suggested spontaneous human combustion. Scully:  Mulder, there are one or two somewhat well-documented cases. [Mulder says nothing, just sort of looks off to the side rather smugly and nods.] Scully:  Mulder, shut up.

If every time a paranormal sounding theory comes out of Scully's mouth (even when she's not necessarily espousing the theory herself but guessing that it may be one of Mulder's) Mulder makes fun of her it's no surprise that Scully would not be inclined to share with Mulder.

General Punkesque Behavior

Teasing Scully when she mentioned spontaneous human combustion.

Juvenile!Mulder strikes again with the ouch comment upon finding the rather large stack of condoms.