People have pulled muscles and dislocated joints trying that.
To quote an unnamed friend of mine: "I love those dreams where you can suck your own dick, and it's so easy."
Also quoting the same friend: "no, dude, every guy has that dream, all the time."
Also quoting that friend: "bullshit man, I can't be the only one having that dream every night."
Quoting me, an hour later: "homie, for the last time, I do not want to hear any more stories about your self-suck dreams."