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1.
Slang for sex or a sexual encounter.

When any sexual act is performed, whether on oneself, with a couple or more, then you are considered to be giving someone a "slice of sunshine"
Paul: Have you seen Sam?
Marc: Yes, he's in the bedroom giving Michelle a slice of sunshine.

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Sam: Where've you been?
Scott: At home mate, giving myself a slice of sunshine.

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Michelle: Last night this dude performed the red eagle on me.
Sam: That is a nasty slice of sunshine.
by Sam Cornwell June 16, 2009