I know you can allow yourself to be touched by an ally, but can you allow yourself to be attacked?
I ask because I would like to use an Injection Spear as an emergency potion for my allies, but my healer has almost no chance of hitting their AC.
Edit: Injection Spear
My ruling has always been that a player can choose to be helpless (Function as Dex 0, and give the attacker a +4 to hit) against an attack, but regardless of that you can't *automatically* hit someone. An eighth of an inch of steel and magical wards don't necessarily care if you want to be hit or not.
Yes, you can choose to take an attack intentionally. However if it's a normal attack, you still have to take armor into account which might block the attack either way. I would treat the ally as flat footed and without their base +10 to armor since they're intentionally trying to be hit. I don't have a RAW citation nor do I think one exists.
Intentionally hitting someone with a normal melee attack is not really covered in the rules, so essentially boils down to "Ask your GM".
There is this though:
Touch Spells in Combat: Many spells have a range of touch. To use these spells, you cast the spell and then touch the subject. In the same round that you cast the spell, you may also touch (or attempt to touch) as a free action. You may take your move before casting the spell, after touching the target, or between casting the spell and touching the target. You can automatically touch one friend or use the spell on yourself, but to touch an opponent, you must succeed on an attack roll.
Which effectively allows you to ignore, among other things, a deflection bonus to AC that would not be under a players control and be effective against touch attacks.
Also consider that all the suggestions of treating your target as helpless, flat footed, dex as 0, are all looking for ways to make it so easy you can really only miss on a 1. I start to wonder whether it is really worth rolling at all.
The only real reason to keep an attack roll is whether you want the risk of a critical hit.
Just some thoughts for your GM to consider.
Why, oh why, isn't there an injection rapier? It would have been perfect for my Elven Reanimator Alchemist.
You rolled poorly on Craft (Weapon) to invent it.
As far as automatically hitting with an injection spear of healing? Yeah, most of these sound good. You mean for the best but that pesky chunk of steel gets in the way. Almost as if it's designed to do that. -5 to AC and flatfooted are probably the best ways to simulate it.
And be careful, you can put an eye out with that thing. (How loudly would you laugh if you injured someone with the weapon for more damage than you healed?)