From the Latin "Bona secunda rsrsrs" this expression is a polite way to greet someone on a Monday. However, this is an ambiguous expression, as it can be said in any day of the week.

Inspecting the morphology of "Bona", "Secunda" and "rsrsrs" we verify they are compound words, respectively, from the words "Bo-na", "Se-cu-nda" and "rs-rs-rs", which are abbreviations for the words:
- Bo -> Bomunus: Translates to "Vamos" in most Peninsulian Iberian languages;
- na: This is a speech mark associated with hesitation (e.g. when a person is nervous);
- Se -> Sexus: Translates to "Sexo";
- cu -> cuntixis: Translating to "Contigus" in archaic Portuguese and "contigo" in modern Portuguese;
- nda -> naxis di assedixs: Translating to "nada de assédio" in modern Portuguese;
- rs -> rixis: Translates directly to "ah", which is an onomatopoeic representation of laughter;

Consequentially, the expression "Boa segunda" means "Vamos sexo contigo, nada de assédio ahahah". Additionally, note that this meaning should only be considered when the expression is proliferated in any day except Mondays. Otherwise, it should be considered a respectful and cordial greeting.

Finally, in a deeper level of wordology, the choice of the first day of the week for this expression is not random, but purposeful. It was chosen, because Mondays are the hardest days in a week, so when someone says "Boa Segunda ahahah", for instance, on a Friday, they are implicitly saying they want to fuck you like a Monday.