The example of situational irony is that at the public house Larry saves his dad from getting drunk by (inadvertently) getting drunk himself. This is definitely not what anyone expected to happen in the circumstances and with the characters of the story and is therefore situational irony. The example of dramatic irony is that the neighbors and Larry's mom all believe that Mick and his buddies intentionally got Larry drunk; however the reader was "there" with Mick and Larry and knows the truth, knows what the characters in the story do not know.
The last example, that of verbal irony, is that Larry's mother calls him a "guardian angel." This is ironic because the image of an "angel" is of an entity--human or otherwise--that does no wrong and brings no evil upon self or others. Larry, his dad's new "guardian angel," was an angel who saved his dad by virtue of partaking in a vice, in other word, by virtue of doing wrong and (temporarily) harming himself. This is verbal irony because it is not what the reader expects Larry's mother to call to him.