A 750 ml beer bottle.  Not my ass, someone else's ass.... And it wasn't my beer, but someone else's beer.  This is what happens when you drink 750 ml of 15% alcohol beer: A mouthy girl says she can sit on it and make it disappear.  And she did.  She put the neck in first and asked for help.  I grabbed the bottom and pushed it half way in and got kinda sick.... Like I was going to throw up but not really.  There were six of us sitting around, but after the bottle was half gone, it was me, a gay dude, and 2 girls.  And don't be so hard on yourself.  Unless you stole from the elderly or punched a child, you're not an asshole :)

I saw a woman insert a 32 ooze beer bottle halfway up her ass.  

I used a glass ribbed dildo up my ass and still do :)  I actually have great creamy cums when I masturbate and have something up my ass !!

I'm 2 submissive to be an asshole actually :)

In someone else's ass?  My 7 x 1-5/8' diameter cock goes into my wife's bum occasionally, but she can't quite handle the entire length.  In mine?  She sometimes warms me up for her 7 x 1-1/2' strap-on by working a Tantus Ryder butt plug into my asshole.  It's a little larger around than my cock at about 1-3/4" in diameter.  The longest item I've had up my ass is a 9" anal bead toy.

As to why you're an asshole?  You'll have to discuss that with your parents.

A finger or thumb nothing more

I have inserted the end of a wiffleball bat up my ass.  It was great!  I also have a butt plug that's a little larger & have done that once & it feels great also.

A flexible dildo more than a foot long (it just disappeared like a Paul Daniel's magic trick.

A surgeon's finger. I think I got off lightly.

Because you're a repressed homosexual who can't come to terms with the fact that his interest in anal penetration comes from an innate to desire for a good hard shag by a big cock? I could be wrong though ...