When I don't have time or when I don't have an iron handy......
I use my hair straightener.
Yup, it works fantastic. I do it all the time. Had a few creases in my tank top this morning and used my hair straightener to get those wrinkles right out.
Please be careful if you are doing this while you are still wearing the shirt. It can be tricky to maneuver. Try not to burn yourself! Also be careful which fabric you are using the straightener on. I always test out a little section at the back of the shirt first.
Am I the only one that does this?