In order to prove to Yuri that they are actually a married couple, Loid and Yor are supposed to kiss. Loid is willing to get this done immediately for the sake of Operation Strix, but Yor can't do this sober, so she ends up downing a bunch of wine and gets drunk.  Yuri sees his sister this way, also gets drunk, and is unable to make rational decisions anymore...
Oh, yes. I've read somewhere that 
your first kiss tastes like lemons.
صحيح. قرأتُ في مكان ما
.أنّ القبلة الأولى لديها مذاق كاللّيمون
Ach, genau, irgendwo habe ich gelesen,
dass der erste Kuss nach Zitrone schmeckt.
¡Es verdad! No recuerdo dónde leí
que el primer beso sabe a limón.
¡Es verdad! He leído no sé dónde
que el primer beso sabe a limón.
Ah oui !
Giusto! Ho letto da qualche parte
 che il primo bacio sa di limone!
Sim! Li num livro que o primeiro
beijo tem gosto de limão...
Ой, точно!