‘To sing ones praises’ means, to praise someone or something with enthusiasm.
For example, “I was only ‘singing your praises’ to the boss yesterday, about how well you were doing in the new job”.
‘The shit has hit the fan’ means, when extremely unpleasant things happen and become known to all.
For example, “While you were out, the bosses came in and ‘the shit has hit the fan’. They want to see you about last month’s accounts!”
‘Boss’ or ‘bosses’ means, employer(s) or supervisor(s).
This is a rude saying, but I make no apologies as it is commonly used in everyday English! Not by all, but sayings like this need to be known and understood. Especially insulting ones. Only so that you know that someone is being rude to you. Or you can be rude to them, if you wish!
There will be some more!