Why Elendil?
 

In Numenor at the time that Elendil was born, the Elendili were being picked on by the King's Men, and it has puzzled me as to why Amandil called his son Elendil meaning elf-friend. Surely that would have just been asking for trouble from the majority of people in Numenor as they hated the elves and those that still dealt with them.

oh probably he wanted to ensure the memory of their ol' friendship with the elves would live in his son and his descendants---naahh, crappy reason!

Amandil seems to mean Friend of the Blessed Realm, and since the Valar were more hated than the elves I think that was riskier. But Amandil was a descendent of Earendel, and therefore akin with the House of Kings. This had protected Amandil's house of the faithful from the wrath of the Kings, and therefore he obviously felt safe enough to name his son Elf-Friend.

Also the language of Quenya that I think the names are in was banned in Numinor, and children did not learn it. I think that they would not necessarily identify Elendil with the elves. Also I think Amandil knew that the shadow would never pass, and perhaps an Elf Friend would be more likely to survive the wrath of the Valar? It worked didn’t it?

It could be that the name Elendil was used only within the family before the Downfall of Numenor and another name, not in the elvish tongue, was used in public.

It's not unusual for members of Royal Families to used different names in different circumstances.

Sure, they were being 'picked on' by the King's Men, but I don't think it ever came to violence, did it? Possibly there were just too many of the Faithful to attack, or that they lived so far away they were not a concern.

I don't think big tall Elendil would've been the kind of guy to not use his own name in public; he was probably quite proud of it.

Amandil and Elendil had been the names of the 3rd and 4th Kings of Numenor respectively. While the later Numenoreans may have lost their reverence for the Eldar, they had not lost their reverence for their ancestors, and giving children the names of former kings was probably not an uncommon practice. As Galorme has already pointed out, Quenya was known by very few in Numenor at that time, so the actual meaning of the names may have not been widely known.

In any case it was no great secret that Amandil and Elendil were part of The Faithful. Rather, it was the fact that they were Lords of Anduine and Amandil's former friendship with Ar-Pharazon that protected them from persecution.

Not to mention the fact the Elendil was almost 8 foot tall!!!!
You don't pick on someone who is twenty inches taller than you unless you are really thick.

Well remember the average size for a male of Anadune (sp?) was nearly 7 foot. Also size doesn't matter, the reason the Faithful weren't treated with violence was because they were also distant heirs to the throne and kin with the kind, and even in a time of persecution family matters.