Lyric discussion by CandyFlip 

Cover art for Nevermind lyrics by Birthday Massacre, The

"Involuntary dilation" could also imply that she was "expanding" her horizons or morals (i.e: having casual sex when maybe that's something she wouldn't often do), but involuntarily because the liquor was what lowered her inhibitions; it wasn't by choice.

@CandyFlip I have a feeling "involuntary dilation" is regarding eyes. Our pupils dilate involuntarily when we are attracted to someone (also with fear and surprise but given the context I'd say it's the attraction)