From the infinitive 'to sible' (pronounced 'sibble'), meaning to perform some form of sexual act with another persons brother or sister (preferably younger for greater novelty value...though not TOO much younger). For clarity in use, the given example would mean that to sible 'her', would be to sleep with 'her' sibling.
'Dude, I would totally sible her...soon as her younger sister's street legal of course.'

'For sure dude! I'd give her the sibling of a lifetime.'
by I Love Grimbling April 13, 2008
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they’re bitches and annoying as hell
Me:My sibling just fricken bit me
My friend:oh well
My sibling: come back here you bitch
by peppapig3790 October 16, 2019
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A person in your family sent from god to punish you for your misdeeds and wrongdoings.
My siblings are really f****** annoying.
by TheWarBroker November 16, 2018
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The people you want to either spend every second with or kill
Guy 1: Dude, my brother is so fucking annoying!
Guy 2: I’m glad I don’t have siblings.
by Jkliopzx November 24, 2018
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They are the human form of hell, younger creatures are selfish and watch Morgz. Older ones are selfish. Don’t have siblings
That other white guy: “I wish I had siblings
Me: “No you don’t”
via giphy
by Hey, I had a grilled cheese March 02, 2019
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