QUOTE (theGuy @ Mar 4 2008, 10:44 AM)

If two people have a chiuv to say a bracha (bracha achrona, for example) and one of them can't say the bracha because he needs to relieve himself, is he allowed to be yotzeh with the other ones bracha? What if only he has the chiuv, can the other person say the bracha for him?
You need to ask your local orthodox rabbi what's appropriate for you in your situation.
That said, look at the last Beiur Halachah to OC 104. The issue is the machloket if "shomei ke-oneh" is mamish like he's saying the berachah. If he is considered literally like saying the berachah himself, then he can't have someone motzee him since his listening is like saying, and if he has to go to the bathroom, then he can't say a berachah, and since listening is like speaking, he can't even listen having in mind to be yotzeh. But what "shomei ke-oneh" means is a machloket, as the Beiur Halachah says.
(That's why, for example, there's a machloket [if I recall correctly between Rashi and Tosefot] if when we are saying the amidah and the shatz starts kedushah, if we carry on with our silent amidah or stop to listen. If shomeiah is literally ke-oneh, then we shouldn't stop to listen since it would be a hefsek. But it's a machloket.)
There are poskim who extrapolate from that Beiur Halachah the lenient opinion that if there is no other choice, and it's a passing mitzvah that you won't be able to make up later, then you can listen to someone else's berachah to be yotzeh if you need to go to the bathroom such that you're not allowed to say the berachah yourself out loud. In other words, one can rely on the opinion that shomeia ke-oneh doesn't mean the listener is literally considered as if he is speaking with all the attendant implications.