From Wiktionary, the free dictionary
- IPA(key): /ˈælæˣ ˈopetɑˣ ˈisæːsi ˈnɑi̯mɑːn/, [ˈælæ ˈ(ʔ)o̞pe̞t̪ɑ̝ ˈ(ʔ)is̠æːs̠i ˈnɑ̝i̯mɑ̝ːn]
älä opeta isääsi naimaan (vulgar) (literally, “don't teach your father (how) to fuck”)
- don't teach your grandmother to suck eggs