Bestia sexy or Sexy bestia may be Italian equivalents of 'sexy beast'. In the word by word translation, the feminine gender noun 'bestia' means 'beast'. The phrase is pronounced 'BEH-stee-ah SEH-ksee'.
Other words may be used instead of the loan word 'sexy'. For example, the adjective 'attraente' means 'attractive, sexy'. The adjective 'provocante' means 'provocative, sexy'. And the adjective 'seducente' means 'seductive, sexy'. In all cases, there's just the one form to be used, be the 'sexy beast' female or male.