please all clear my chat History

Pretty much no way to do that.

if you are talking about your inbox
http://mingle2.com/inbox/list
you can check mark the boxes , then way down at the bottom delete selected

but if i remember right , that only deletes your side of it
cause i have friends on here that do that (at least that was me guess , cause there side of the convo went blank), makes the email looks like i have been talking to meself the whole time(cause me text is still there in the email) lol
nothing new , i just don't normally take the time to type it out while i am talking to meself <shrug> : )

as far as forum history , yeah no idea there , i never wanted to delete anythen from there

any who , hope it helps

It would be a nice option thou !!