The story of Pyramus and Thisbe is a tragedy; it's about the star-crossed young lovers who kill themselves needlessly. That makes it lamentable, or sad. The "comedy" is that Bottom and the other players are very bad actors and they have put together a very bad version of the play. Their presentation is so bad that it is funny and therefore, a comedy. When Theseus reads the description of the play, in Act 5, sc. 1, the play is referred to as being "tragical mirth", which are opposing terms just like "lamentable comedy". The irony is in these opposing terms.
The irony with Pyramus and Thisbe being a lamentable comedy is, because the true purpose of the play is that it suppose to be a Greek-like tragedy between two star-crossed lovers. But because the actors, script, and setting were horrendous the audience took it more as a comedy than a serious drama.
Despite the fact that they loved eachother so much they could never be together because of Pyramus's assumption of the death of Thisbe. Both commited suicicide in the end becuase of there love for eachother. It is considered a comic tradgedy because of thier ignorance and yet thier willingness to sacrifice there lives for one another.
the humor results is not just because bottom is ready to play the roles but also because of the nasal twang when he prounces "thisby" as "thisne"
In ActI sc.2. Quince declares that they are going to stage: "The most lamentable comedy, and/ most cruel death of Pyramus and Thisby."
Situational Irony: 'Lamentable comedy' is an oxymoron and clearly underscores the incongruity of the choice of a tragedy to be staged during the wedding celebrations of Theseus and Hippolyta.
Verbal Irony: results when Bottom suggests that he play both the roles of Pyramus and Thisby simultaneously:"let me play Thisby too I'll/ speak in a monstrous little voice. 'Thisne,/ Thisne; Ah pyramus lover dear! thy Thisby dear, and lover dear." Act I Sc.2. The humour results not just because Bottom is ready to play both the roles but also because of the nasal twang when he pronounces 'Thisby' as 'Thisne'.
Dramatic Irony: The intertext from Ovid's "Metamorphoses" would have been familiar to a Shkespearean audience. They would have enjoyed Shakespeare's hilarious parody, even as they would have straightaway recognized the parallels between the Pyramus Thisby story and the stories of the lovers of the main play.