"Tynf" was a colloquial name of a coin made in the 17th century in Poland. In that time the value of money was equal to the amount of metal used for its production. Which basically means there was a space for creativity for those who wanted to earn some money by simply using less silver than they should (ie be able to buy more for less). So this particular coin was a perfect example of a swindle - it was worth anywhere from half to two-thirds of its price. So originally this saying was sarcastic and aimed at the state and its ruling more than at the joker. Today, I haven't heard anyone use it, but I suppose people might not know what a "tynf" is and assume it's something valuable while it's the opposite. So I would suggest not using this saying as it is unclear whether it's sarcastic or whether it simply means "it's always good to hear a fine joke".

W skrócie oznacza to dobry żart. Powiedzenie odnosi się do waluty Polskiej - 1-tynf. W 17 wieku żartowano z tej waluty, bo była niedbale wykonana i miała zawyżoną wartość odnośnie wartości rzeczywistej.

Dzień dobry :), To jest przysłowie obecnie mało znane. Oznacza po prostu, że opowiedziany żart/dowcip jest dobry. Tynf to nazwa starej monety z XVII wieku, której wybicie (pojawienie się na rynku) było pewną pomyłką (żartem). Można więc uznać, że usłyszany żart, jest tak samo śmieszny jak pojawienie się tej monety.