Start by picking a random number between 0 and 31. (A-Z, 0-9, and take away 1, 0, I, O). Append that character to a string. so, g then h then j etc. You'll have ghj5jkg4 using the above example. Check that string for inappropriate language. You don't want to randomly generate something like 1fuck3r5. As suggested in the comments, removing just vowels may be sufficent, especially if you don't use numbers.