I thought from our contact over 11 months - and I haven't told you any details of that - that he was as way out as me.
What you don't seem to grasp is that tipping sheep shit in someone's face IS NOT funny or way out. When you add in that this was pre-planned (you went equipt in armed robbery terms), it is really really strange and abnormal behaviour.
The fact you keep insisting that some "way out people" on your wavelength would have found it funny indicates that you really are not in touch with typical human reactions. I think it is probably this aspect of your posting that has lead people to query whether you have Asbergers/autism - because by this insistance on this you are showing a lack of empathy with an expected human reaction.
To answer your question about how to repair the friendship I think the only thing you can do is apologise properly and fullsomely and mean it (you may have struggled with the latter given what you have posted here) and then DO NOT MENTION IT AGAIN. If you keep going on about it, you are just rubbing his nose in it so to speak.
If you are lucky, you will have opportunities to see him again and with the passage of time it may fade in his mind provided you don't do anything so gross or crass again.
TBH though you may have to accept this is irrecoverable. If someone did that to me, I would not want to be friend's with them -
not specifically because of what they did (ie. a recipient of sheep shit) although I wouldn't like that!!! -
but the fact that they pre-prepared and came with the sheep shitt (gave it some careful thought & planned it) and then thought it was an appropriate thing to do - would mean I would judge them as having very very poor judgment and behaving in such a socially perculiar way that I wouldn't want to socialise with someone like that or to have them in my life. Life is too short.
Keep your head down and don't mention it again and you may be lucky. I doubt it though. I think that goose is cooked.