Somebody who hasn't reached any "bases" yet, somebody who has been single their whole life or is currently single
"Bob is a benchwarmer... He hasn't even gotten to first base yet!"
by ALonelyKea June 8, 2017
"Get Tim on the phone, or else he's gonna miss his go on the beer bong"....."Already tried him... he's not coming out tonight, the f!#*&@! benchwarmer"
by TheAthlete November 2, 2014