Presumably you'll make a glass stick, or else an emergency room visit, depending on how hard you suck.
Glass blowing is clearly going to replace most manual jobs in the 1940-50s. If you are one of those unemployed chimney sweepers you should look it up.
No matter how hard you try, you absolutely will create a bunch of chunky, ugly cups akin to elementary school arts and crafts. Also like elementary arts and crafts, it’s a lot of fun.