Birsay's baptismal register of 1751 yields much more information to the family historian:
Septr 29th To George Anderson in Swaneyside (a scoundrall a knave a scrub a Rascall a Villain a cheat) a son called Andrew.
N.B. he had been in the Northwest & has been three years in Wascra
(Wascra is a farm in Birsay)
Underneath the slur is written in another hand:
the above George Anderson is as honest, just, obliging man as any other man in this parish.
...which suggests either that the character of George Anderson divided opinion or that all the men in Birsay at that time were a bunch of scrubs.
I had come across the insults villain, scoundrall and knave before in the archives but not scrub. I looked it up in the Scottish National Dictionary for your information:
scrub /skrub / n a guy that think he's fine and is also known as a buster. Always talkin' about what he wants. And just sits on his broke ass