Before I Self Destruct 50 Cent
Michael Myers is the name of the serial killer from the "Halloween" series of horror movies. Here, Fiddy warns us that when consuming cough syrup, he becomes similarly dangerous.
ICU is an abbreveation for Intensive Care Unit in the hospital. This is usually where patients go when they are dying. So he believes they go to heaven when they die. The last place they are before they die is the ICU in the hospital.
Mr. Cent is saying that if you are in the Intensive Care Unit he will visit you, and kill you.
Mr. Cent is pretending that "they" have pulled off a lot of crimes and haven't gotten caught. Even though he sued an advertising company for $1 million for using his face on an internet ad that said "shoot the rapper and win ringtones"...
What Mr. Cent is referring to is that a Crime Scene Investigator is trying to determine who killed someone with a fire arm; but alas they cannot find a fingerprint, the unique pattern on the tips of your fingers left behind at most crime scenes.
50 is suggesting that he is such an expert criminal that would not leave any fingerprints on any weapons he may have used in the past
An ICU is an Intensive Care Unit, saying he will put you there, then watch you die.