It means:
un·der·ming /ˌʌndərˈming or, esp. for 1, 2, 4, ˈʌndərˌming/ Pronunciation Key - Show Spelled Pronunciation[uhn-der-ming or, esp. for 1, 2, 4, uhn-der-ming] Pronunciation Key - Show IPA Pronunciation
–verb (used with object), -mined
1. to not get laid on their honeymoon
2. Ed