verb: to not follow through on plans previously established with no real or sudden reason, often but not necessarily last minute, after:
1) multiple confirmations, 2) hinting/asking to be invited to plans already in motion by others, 3) initiating said plans, 4) telling third parties about those plans, 5) expressing excitement about the plans on multiple occasions, or 6) any combination of 1-5.
Multiple showings of a "weiny out" make one a "weingarten", and a "weingarten" who frequents the "weiny out" option 6) is a "tecumseh sherman". The only known species of tecumseh sherman resides in Newport, CA.
background: many "weiny out" linguistic experts believe that this term is just a synonym for "flaking out". While it is true, they are similar; there are two important distinctions.
Firstly, they have clearly given some sort of indication that they will not "flake out", as exemplified in #s 1-6 in the definition. And secondly, the "flake out" must also be for no new or important reason, ie "I'm tired".
Sometimes there is a prolonged "weiny out", i.e. "I'll text you when I'm leaving to get there" (and then not show up). This is called the "heyyyyyyyyyyyy guys"
Bubba: Yo bro, I know youre coming to my place to pre-party first, but what time did you want to head out to the club?
Terrico: Nah man, cant make it tonight.
Bubba: Ya gonna weiny out on me now? I just took a shower and am three shots in.
La'donte: Hey how do you get to the place where the birthday is at?
Pernell: Oh, I aint going.
La'donte: Wow, did you just weiny out on your own birthday dinner? Unreal!
Important note: If a known weingarten or even THE tecumseh sherman follows through on plans and you "weiny out" on the same plans then its called a...well, its never happened so there isn't a name yet.