偏偏 (of all things / just had to)

Of all days

• You planned the class picnic for weeks. It has been sunny all month — until today.
• we / us我们wǒ menwith great difficulty好不容易hǎo bù róng yìto fix定dìng(completed / change)了lepicnic野餐yě cān(modifier / structural particle)的deday日子rì zi，insisted偏偏piān piānthat day那天nà tiānto rain下雨xià yǔ。 — "We finally fixed a date for the picnic, and of all days, it rained."

insisted偏偏piān piān = of all things, just had to

• insisted偏偏piān piān marks that something happened against what was wanted or expected, often annoyingly: insisted偏偏piān piānthat day那天nà tiānto rain下雨xià yǔ.
• It can also mean "insist on (doing the opposite)": told让rànghim他tānot to别biégo去qù，him他tāinsisted偏偏piān piānon要yàogo去qù.

told让rànghim他tānot to别biégo去qù，he他tāinsisted偏偏piān piānon要yàogoing去qù。

Bad luck and stubbornness

• Bad luck: I我wǒurgent急jí(ongoing -ing)着zheto go out出门chū mén，the keys钥匙yào shiinsisted偏偏piān piānto try to find找zhǎonot to arrive不到bú dào(completed / change)了le。 — "I was in a hurry, and of course I couldn't find my keys."
• Stubbornness: everyone大家dà jiāall / both都dōuto advise劝quànhim他tā，him他tāinsisted偏偏piān piānnot不bùto listen to听tīng。 — "Everyone tried to persuade him, but he just wouldn't listen."

I我wǒin a hurry急着jí zheto go out出门chū mén，the keys钥匙yào shiof all times偏偏piān piāncouldn't find找不到zhǎo bu dào了le。

It needs a contrast

insisted偏偏piān piān versus surprisingly竟然jìng rán

• surprisingly竟然jìng rán = surprisingly (any surprise).
• insisted偏偏piān piān = contrary to what was wanted — frustrating timing or stubborn behaviour.

he他tāsurprisingly竟然jìng ráncame来lái了le。

Recap

Read the full reference: HSK 6 grammar — Adverbs.