what would you call someone who always focuses on the irrelevant bits during an argument...?
someone who, if you said, for instance - "when you went to your mums at lunchtime i asked you to pick up my scarf that you left there, i told you it was very important and you didn't get it" - and their response is (shouting) "i didn't go there at lunch time, i went at about 2pm!" ...
and generally argues about minor facts that don't matter at all, and change nothing in the row.
i don't mean someone who is using deflective techniques, to try to spin the row around onto the other person, or to change the subject, or to stall for thinking time, but someone who is genuinely just being pedantic about 'facts' and gets hung up on them being correct
not bombastic
"ostentatiously lofty in style; "a man given to large talk"; "tumid political prose".
not sententious
"Given to moralizing in a pompous or affected manner."
not pretentious
"Attempting to impress by affecting greater importance, talent, culture, etc., than is actually possessed."