A person may feel satisfied or pleased when they d something bad or unfair to you, but if you can get revenge, you will feel more satisfaction.('He who laughs last laughs best' is also used, and 'he' is sometimes omitted.)
To do something nice or kind to someone who has been nasty to you. If someone felt bad because they forgot to get you a Christmas gift, for you to buy them a specially nice gift is heaping coals on their head. ('Heap coals of fire' is also used.)
If you hear something on the grapevine, you are informed about something by someone, circulating information or gossip from one person to another informally.
('Hear it through the grapevine' is also used.)
(UK) If a machine or system is described as Heath Robinson, it is very complicated, but not practical or effective, named after a cartoonist who drew very complicated machines that performed simple tasks.