！！
Pbbbbt! Serves you right for making fun of a lady!
Literal
[raspberry]-[copula-だっ]! Maiden [obj-のことを] sneered-at punishment [emph-よ]!
ベェーだ is a childish/playful raspberry sound (sticking out the tongue and blowing) used as taunting defiance. 嗤う is a rare-kanji variant of 笑う specifically for derogatory / sneering laughter — the rare form is chosen to flag the hostile sense and keep it distinct from ordinary friendly 笑う. ~のことを literally 'the matter of X' with を softens a direct object and is common when the object is a person.