參加活動認識了很多新朋友，對其中的一兩位還有興趣多了解一下，于是，就主動搭訕了幾句。結果，人家被這熱情嚇到，立馬順口提及自己的男朋友/女朋友，暗示你不要再靠近。

Boyfriend/girlfriend drop refers to the act of subtly adding the fact that you have a boyfriend/girlfriend into the conversation in order to deter anyone who is potentially interested in you.
“扔男友/女友”指在聊天的時候不經意提起自己有男朋友或女朋友的事情，目的是為了擊退某個對你感興趣的人。

For example:

She thought I was interested in her and boyfriend dropped me in our last meeting.
她以為我對她有興趣，于是在上次見面的時候就告訴我她有男朋友了。

這個說法大概是來自于英語中另外一個使用較廣的表達name drop，名詞形式為name dropping，也就是我們平時說的“拽人名”。

Name dropping is the practice of mentioning important people or institutions within a conversation, story, song, online identity, or other communication.
Name dropping指在談話、故事、歌曲、網絡身份或者其它交流中提及重要人物或機構的行為，即“拽人名”。

Name dropping is used to position oneself within a social hierarchy. It is often used to create a sense of superiority by raising one's status. By implying (or directly asserting) a connection to people of high status, the name-dropper hopes to raise his or her own social status to a level closer to that of those whose names he or she has dropped, and thus elevate himself or herself above, or into, present company.
“拽人名”通常是為了在某個社會層級中確立自己的地位，通過提高自己的地位來建立一種優越感。這些人在暗示（或者直接表明）自己與高層人士的關系時希望能夠將自己的社會地位提升到與那些高層接近的狀態，從而凌駕于身邊同伴之上，或者成為與其平等的一員。

（中國日報網英語點津 Helen）