Of course you can, you can do anything "outside of combat." You only need to roll initiative when it becomes important who goes first.
The reason that you don't always have everyone with an attack held is that standing ready to smack someone is a decidedly unfriendly way to go through your day, and will wreck your social interactions, you can only hold and attack for a reasonably specific trigger, and you can get more done with an action than with a held attack on your reaction.
In many circumstances, if a player declares that he's holding an attack ("I'm holding my crossbow on him--if he makes any sudden moves, I'm squeezing the trigger,") it's probably time to roll initiative anyway... but not necessarily always.
This isn't a video game. There's no "in combat" or "out of combat," there is just narrative speed vs. initiative order. Also, Mexican standoffs can and do happen.