When I get on the mic I'mma snap
Make you wish the ambulance that took me to the hospital
When I overdosed woulda caught a flat

from Eminem (Ft. X Ambassadors) – Wicked Ways Lyrics on Rap Genius

Meaning

Other rappers know that when Em gets on the mic, it’s sure to be something crazy. They could never be as good, so this makes them wish the ambulance Eminem was in would have gotten a flat tire. In other words, they wish he would have died.

In an interview Eminem spoke about his overdose:

[Doctors] said I was about two hours from dying

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