glad hand

Short definition from Wiktionary

Noun

1. 1
   A warm welcome offered to a guest by a host.
2. 2
   A coupling device used on semi-trailer trucks for attaching air brake lines from the tractor to the trailer.

Verb

1. 1
   To be overly friendly with (a stranger) in order to gain an advantage.
2. 2
   To extend a glad hand (to someone); to welcome warmly.