By decelerated do you mean a 5-year plan? I believe NYCOM does if you have extenuating circumstances. PCOM allows you to remediate classes, but all medical schools basically allow for that to some extent.
Osteopathic schools are not decelerated, although some offer decel programs. Actually at some Osteopathic schools we learn much more information in our 1st 2 years than most allopathic schools. At NYCOM, 1st and 2nd years go to class from 8-5 most days of the week and 8-3 or 8-12 once or twice a week at most. My allopathic friends go to class 8-12 almost every day of the week! Plus we take classes in our 2nd year that most allopathic students don't take until their 3rd and 4th years. If anything, I'd say some osteopathic schools are ACCELERATED, not decelerated.
As for the reasons we're made fun of...I really am not sure exactly. Probably because it seems easier to get into a DO school than an MD school. The people making fun of DOs tend to be people with little knowledge of and very little experience with osteopathic medicine.