Picture a surface with points standing out of it: a , a chestnut case, the top of a fence. That is the whole word. Spike is a long pointed nail, and -y means 'having that quality', so spiky is 'covered in points'. Hair can be made into points in the same way. A person, a song or a piece of writing can feel like points too — instead of a smooth surface, you keep meeting small sharp ends.
The source traces this spiky to spike 'a piece of pointed metal' plus the adjective suffix -y, with spike itself going back through Middle English for a large nail. So the modern word can be read straight off its parts: having spikes.
來源把這個 spiky 拆成 spike（尖銳的金屬物、長釘）加上形容詞字尾 -y；spike 本身則可追到中古英語，指大鐵釘之類的東西。所以這個字可以直接從零件讀出來：帶著尖刺的。
Wiktionary entry for 'spiky', etymology 2 — etymology_text supplied in this evidence packet (source_ref kaikki:3f6f69a190036ae4:1385001808)
From the picture
把尖刺搬到感覺上
這兩個意思都是比喻：尖端不在表面上，而在你跟對方相處、或在你聽和讀的過程裡。共同點是「碰到的不是平滑的表面，而是一下一下的小尖端」。
adjective · C1
Describing a person who is easily offended or annoyed, and who can be sharp and hard to get along with. This use is informal and is heard mainly in British English.
易怒的；帶刺難相處的
adjective · B1
Covered with long sharp points, or shaped into them — like a cactus, a chestnut shell, or a fence with pointed tops.
有尖刺的
adjective · B1
Spiky hair is cut short and made to stand straight up in stiff points, usually with gel or wax.
（頭髮）豎起成刺狀的