Whilst having intercourse from behind (usually doggy style) the act of inserting a thumb in your partners rectum, then proceding to take it out and suck on it.
Cody : I was fuckin this chick hard doggy last night and I had the best arizona thumbsicle of my life
Taylor: You're a sick fuck. But I dig it!
Taylor: You're a sick fuck. But I dig it!
by Up and in April 22, 2009
In an attempt to prevent thumb sucking one inserts the suckers thumb in to an ass (not the suckers ass) and creates a nasty tasting treat.
While my girlfriend was sleeping I inserted her thumb up my ass creating a thumbsicle as an attempt to prevent her from sucking her thumb.
by jakjonz May 29, 2014