It all depends whats on them. If you talking people's personal photos, names or personal details like baby weights and dates, just bin them.
If its non personal and just a standard mug you print and sell with your design on, then when i first started and made several mistakes i gave them to a local charity or cafe. However now both the local charity and cafe have me print mugs up for them.

As someone has already said tho. Its your time and money wasted so bin them. Do you really want to give poorly printed mugs away that represent you / your company? If you do choose very carefully who you give them to.