[Engineer]

Lots of undergrads blow off freshman year so you wouldn't be the first one he's seen. Admit to the alcohol problem (don't mention the coke), mention you're sober x months and attending AA meetings or something along the lines IKE mentioned above, hint at an unspecified personal problem that drove you to drink but is now resolved, stress your determination to make things right and request a second chance, perhaps another semester of probation with an even higher GPA required to get off probation? Don't overthink your dress and grooming just be comfortable and professional, and be authentic when you say "I realize now what a huge mistake I made and really want to do things the right way" Good chance he won't turn you down. Hopefully you didn't have other discipline problems (campus police) that he knows about. Attend a time management lecture/read a book, so you can show him you're addressing that as well. Don't suck his dick about bioengineering unless that's something you are truly interested in.