One thing lead to another
The phrase 'one thing lead to another' is typically used as an excuse to justify the act of having a one night stand with a complete stranger(s).
Jennifer: So I met this guy at this party, and we were having such a great time getting to know each other, and before we knew it one thing lead to another and ...
Lily: Did you get his name and number?
Jennifer: ...
Lily: Did you get his name and number?
Jennifer: ...