走就走，别……: fine, but don't…
【高127】紧缩复句 / complex sentences
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
V (+ object) + 就 + V (+ object)，别……: the speaker lets the action happen ("if you want to V, then V") and at the same time forbids a reaction or attitude that goes with it. 走就走，别用这个威胁我: "leave if you want, but don't use that to threaten me". The verb (with its object) is repeated on both sides of 就, then comes a clause with 别.
The tone depends on the situation: defiance (走就走，别……), reassurance (领导说几句就说几句，别太在意), resignation (加班就加班，别抱怨). The same mould also says "one thing at a time": 吃饭就吃饭，别老看手机 (when you eat, just eat).
Do not mix it up with 别 + a bare verb (HSK 1), which forbids without conceding anything, or with X就X吧, which accepts without forbidding anything. It is not a condition either: 就 does not mean "then" as in 如果……就……, and you do not put 如果 in front. Register: spoken.
Examples
买就买，别犹豫了。
Mǎi jiù mǎi, bié yóuyù le.If you're going to buy it, buy it; don't dither.
输就输，别找借口。
Shū jiù shū, bié zhǎo jièkǒu.If you lose, you lose; don't make excuses.
加班就加班，别抱怨，谁都累。
Jiābān jiù jiābān, bié bàoyuàn, shéi dōu lèi.Overtime it is, then, but no complaining: everyone is tired.
走就走，别用这个威胁我！
Zǒu jiù zǒu, bié yòng zhège wēixié wǒ!Leave if you want, but don't use that to threaten me!
领导说几句就说几句，别太在意。
Lǐngdǎo shuō jǐ jù jiù shuō jǐ jù, bié tài zàiyì.If the boss wants to say a few words, let him; don't take it to heart.
吃饭就吃饭，别老看手机。
Chī fàn jiù chī fàn, bié lǎo kàn shǒujī.When you're eating, just eat; stop looking at your phone.
Common mistakes
✗ 加班就是，别抱怨。 → ✓ 加班就加班，别抱怨。 (the verb is taken up again on both sides of 就; 就是 has another meaning).
✗ 如果加班就加班，别抱怨。 → ✓ 加班就加班，别抱怨。 (it is not a condition: no 如果 or 要是 in front; only 要 stays possible, as in 要走就走).