A radish. And in slang, a terrible actor.

What a Japanese person actually thinks
Vegetable first, bad-actor joke second. Both readings arrive instantly and neither is what you were going for.

Literally: big + root
Actually: The white daikon radish. Also 大根役者 — 'daikon actor' — the standard Japanese insult for someone who can't act.

Naturalness●●●●●

Correct Japanese for a root vegetable.

Coolness●●●●●

The characters do genuinely read as 'big root', which is presumably the trap.

high大 (big) and 根 (root) are both fine characters. Together they are exclusively a vegetable. Kanji don't compose the way you'd hope — the compound has its own fixed meaning.

根 ne
root; origin; foundation

Alone, 根 does carry the metaphorical sense of roots and grounding. It's the compound that ruins it.

大根

Orientation: either

N/A.