When you don't know the full story but you believe what you know is right.

To be assuming all the time.

assume = to make an 'ass' out of 'u' and 'me'.

The mother of all fuckups

to make an ass out of u and me.
verb. To believe something is true based upon general unproven observations and reports.
Coining up a foolish, humorous insinuation about somebody or something that is probably not valid.
To make a complete idiot out of yourself or another person by saying that something happened that didn't.

When you ASSUME means that you make an ass out of you and me.

a person with a tendency to jump to conclusions without proof or evidence.