Two common defenses against DUI charges are: Driving badly does not necessarily equate to DUI, and physical appearance does not equal DUI.
Imagine this scenario: It is 5 a.m., and college student John has just left a friend's house where he had been studying for exams from 7 p.m. to 5 a.m. They had a few beers, but the last one John had was a few hours ago. His eyes are red from exhaustion and allergies, and his hair is unkempt. His clothes smell slightly and have a few pizza sauce stains. On the way back to his apartment, he reaches down to change a song on the radio and drifts into the next lane. The next thing he knows, he is being pulled over and charged with DUI.