This phrase is not exactly slang but a colloquial expression, mostly used in Spain. 'A mi plin' means 'I don't care' or 'It doesn't bother me'. 'Y a la madama dulce de coco' is not a common phrase and its meaning might vary depending on the context, but it could be interpreted as a playful or humorous way to refer to someone, possibly a woman who is sweet or pleasant.
Examples
- Spanish: 'A mi plin que no te guste mi estilo, y a la madama dulce de coco también.'
- English: 'I don't care if you don't like my style, and neither does the sweet coconut lady.'