I've had SFO miss things that really shouldn't have been in my carry-on on numerous occasions, it's pretty lax as far as US airports go.
I wouldn't worry about getting held up for a few hours by TSA, or anyone else for that matter, unless you actually give them a valid reason.
Hell, I even had a locking knife confiscated by security in belfast, and apparently in Northern Ireland that's a class A weapon! (whoops)
I mean, I had it to cut cheese and spread mustard, and it was obvious that I wasn't IRA, so the police just made me fill out a form and let me go - in about 10 minutes - with a warning that possession of a class A weapon carries up to a 10 year sentence! *phew*
So yeah, people worry way too much about airport security- take it from someone who gets searched much more often than the background population because of the way I look and has been on probably 100 flights all over the world since 9/11 - and accidentally had tons of stuff confiscated, from spoons to screwdrivers to knives (living out of a backpack
). You're never going to be held up for hours over an e-cig unless they're illegal in the locale, like HK, and even then it's unlikely if you're just a visitor.