At the start of a line, だって is an excuse: “but…”, “well, because…”. だって眠いんだもん = “but I’m sleepy!”.
Casual. It can sound defensive, like making an excuse; in a meeting, use というのも instead.
A comedian is told the other person will date them if they win first place in tonight's audience-voted show.
Culture note In Japanese comedy duos, your partner is your 相方 (aikata), and a duo can't do its act alone.
'Cause my partner isn't here today!
Textbookなぜなら、今日は相方がいないからです。Line-initial 'だって' replaces 'なぜなら', and explanatory 'んだよ' replaces '〜からです' to give the excuse.
One performer earnestly presents a theory about why God gave humans five fingers.
Because if you just needed to hold it any old way, two fingers would do.
Textbookなぜなら、適当に持つだけなら指は2本で十分だからです。Textbook 「なぜなら〜からです」 shrinks to line-initial 「だって」, and the closing 「から」 is dropped entirely in speech.
Two performers are debating what counts as cute, and one claims being completely naked is cuter than candy.
Well, because you might get arrested.
Textbookなぜなら、捕まる可能性があるからです。Textbook 「なぜなら〜からです」 becomes casual line-initial 「だって〜から」, a quick 'well, because…' defending a strange claim.
Someone has been called a flasher and wants to know what that's supposed to mean.
Because you're a flasher!
Textbookなぜなら、露出狂だからです。Line-initial 'だって' replaces 'なぜなら', and explanatory 'なんですよ' replaces '〜からです' to justify the claim.
A son warns his mother that a gateball tournament organizer cheats players, then asks why she still enters his matches.
Culture note Gateball is a croquet-like team sport that is very popular among elderly people in Japan.
Well, because... um...
Textbookなぜかと言いますと、それは、その…「だって」 replaces textbook 「なぜかと言いますと」, opening a flustered excuse that trails off into the fillers 「それはその」.
From other routines in the library. Automatic transcripts, not yet checked line by line.
だって means “but… / because…”. At the start of a line, だって is an excuse: “but…”, “well, because…”. だって眠いんだもん = “but I’m sleepy!”.
With friends: OK. With coworkers: careful. With a boss or teacher: avoid. Casual. It can sound defensive, like making an excuse; in a meeting, use というのも instead.
In 1,905 live comedy routines, だって appears in 362 lines from 129 comedians.