When it comes to undercooked meat there are things you can get away with and there are some things you most certainly can’t.
Poultry should always be cooked throughout with no pink juices. This is because it carries bacteria right the way through the flesh that can only be killed by heating for a good amount of time. Pork is a similar case and I would never eat underdone pork. The risks can range from a mildly jippy tummy to life threatening food poisoning and possible death.
Smoked and cured meat is sometimes raw. Smoked salmon or Parma ham for instance, the bacteria has been killed in other ways. This is a high risk food though and correct storage and monitoring of the shelf life is a must.
Beef and lamb are slightly different. You can get away with pink inners because bacteria only lives on the outside of the joints. However, controlling any contamination form the outside of the meat to the inside is a must. Always use separate utensils for raw and cooked meat. If you have any doubts, always cook meat through and never leave anything out of the refrigerator for longer than 30 minutes, less on a hot day. Beef mince should always be cooked through.
Yes, some people do sear fish or even eat it raw but these people also know what they are doing. The fish has to be incredibly fresh and you must know where it has come from. Get expert instruction on this or leave it to the professionals. Never take any risks with children or the elderly as they have lower immune systems. Always defrost meat well before cooking as you may leave cold spots otherwise that are not cooked.