Most dildo type (penis shaped) vibrators can be inserted in the ass, but you
shouldn't insert anything in your ass that doesn't have a flange or wide
base at the bottom that will keep it from going all the way inside you. If
you want to combine anal stimulation and vibration, use a vibrating probe
especially designed for anal use, or a vibrating butt plug.
Dildo-shaped vibrators should not be used for anal insertion if they do not have a flanged base or something at the bottom end that will effectively stop them from going all the way into the asshole. If a vibrator does go all the way into your rectum, it is possible for it to get stuck in your colon, and it may require a very embarrassing trip to the emergency room to get it out. There are a variety of safe vibrating anal toys available that are specially designed to avoid this risk, including vibrating
butt plugs, anal beads, and anal probes.
If you have a plug-in vibrator, obviously you're in no danger of losing it up your ass, but you may have trouble getting it up there in the first place. You'll probably need to purchase special attachments for vaginal or anal insertion. Attachments are available for both the
Hitachi Magic Wand and coil-type vibrators that resemble dildos or rippled anal probes.
Whenever you insert anything in your ass, use plenty of lube. Water-based
lube is compatible with all vibrating toys and attachments.