A D28 case will fit in most overheads. There are a few exceptions - mostly on older planes. It takes up almost all the room, so your kind of being an asshole, but no more so than anyone else on most flights. If it doesn't fit, ask the flight attendants if you can put it in the coat closet. They frequently will let you do so. It is absolutely the way to go, if you can do so. The most important thing to remember is to ALWAYS be polite with the folks at the airport and the airlines. Also, get on the plane as early in the boarding process as possible, or there won't be room for your guitar.
Light
"Cowards can never be moral."
M.K. Gandhi