Steplingus
Finding out, typically when one or more of the parties are in a drunken stupor, that a step-sister has had a secret crush on you for some time. Typically the lush involved uses words like "probe" and "hot" as they slur out their heretofore private lust. The recipient of these unwanted advances struggles to escape the ranting, slathering monologue. Future gatherings and holidays can be particularly awkward, especially since other family members (siblings) who witnessed the horrific event typically know what the drunken strumpet confessed to...even though she may not remember.
Dude...my step-sister Kelly totally pulled a steplingus on me...she told me how she always thought I looked HOT, especially when I used to drive my old Ford Probe. She said she wanted me to probe HER. Her breath smelled like she tossed salad. I had to swallow my own vomit before I could escape from her drunken confession. I can't sleep anymore from the nightmares.