Rugi = waste, or lose out
Two different meanings...
But, they mean the same, at least in one usage in the context of Bahasa
And do remember, 'sayang' is also used widely as reference to your loved ones (in place of you or I).
In one context, we may use the word 'sayang' in expressing the feeling that we will lose out (or it's such a waste) for not doing somethin. As an example, one may say, "Sayang (kalau) tak sambung belajar sementara masih muda." (It's such a waste for not furthering our studies while we're still young).
Unfortunately, one may misinterpret the sentence, which would then read, "My loved one (he/she) doesn't further his/her studies while he/she is still young."
I always make fun of this whenever joeperantau, while chatting, uses 'sayang' (as in it's such a waste) because I'd rather use 'rugi' which makes more sense, "Rugi (kalau) tak sambung belajar sementara masih muda."
Example of a dialogue between joeperantau and myself:
Location - joeperantau was in a hotel room in New York while I was at home in Shah Alam.
deoughtred: Joe, kau tak tidur lagi ke dah lewat ni?
joeperantau: Dah sampai New York ni. Sayang aku nak tidur ni.
deoughtred: Sayang? Kau bawak awek balik hotel ke Joe?
(he didn't answer my question, instead he gave me a middle finger via webcam)
deoughtred: Ooo... maksud kau, rugi nak tidur (alang-alang dah sampai New York)
Whether it makes sense or not, 'sayang' is acceptable as an alternative to 'rugi'.
So, if you're tired of calling your loved one honey or darling or sweet-pea or cutie-pie, why don't consider calling him/her 'rugi'.
Imagine this, when you just came back from work and you open the house door and say.... "Rugi, I'm home!" or translated as "It's such a waste (that) I'm (back at) home!" And expect your spouse/partner won't let you sleep in the bedroom for the night.