From Longman Dictionary of Contemporary Englishbe my guestbe my guestspokenLET/ALLOW used to give someone permission to do what they have asked to do ‘Do you mind if I look at your notes?’ ‘Be my guest.’ → guest
Examples from the Corpus
be my guest• Oh, hell, be my guest.• "Do you mind if I sit here?'' "Be my guest.''• "Is it all right if I call my parents?" "Be my guest."• "Could I use your phone?" "Be my guest."• For the moment you are my guest.• You were my guest, remember? 