It can mean to eat a huge amount, more than you normally would.
Mess
Guinea pig is not an idiom. It is a type of small rodent that is often kept as a pet.I have a pet guinea pig.
The idiom "happy as a pig in a wallow" means being extremely content and comfortable, like a pig rolling around in mud or water. It suggests a sense of total bliss or satisfaction in one's current situation.
This isn't an idiom because you can figure out what it means without someone telling you. When you see "AS ____ AS _____" you're looking at A Simile - a type of comparison. They're comparing someone's happiness to the happiness of a pig wallowing around in the mud.
Medicines and other things are often tested on small animals. Being a guinea pig means things are being tested on you or are asking you to try something out.
It means eating an excessive amount, much more than normally a person would eat.
To "pig out" means to eat excessively during a meal. "I am so full! The buffet was so good that I just had to pig out!" "We are all so sick because we pigged out last night."
The idiom "bleed like a stuck pig" refers to the fact that pigs will bleed a lot when stabbed. It originated to make a point about vulnerable people.
The idiom is "when pigs fly". Bacon comes from pigs, but bacon is not in the idiom. The idiom simply means, "impossible".
The idiom means that the person over-indulged in whatever food or drink was provided, consuming more than was polite or prudent.
It is not an idiom, it means your nose is itching.
It's not really an idiom. It means "what are you thinking about."