Just rewatched S11’s “Deadly Courier” and, boy, did Danno have a shark jump in that one (Mcgarrett’s still jumping from “Invitation to Murder” at this point). McGarrett specifically tells Danno to “use a cover” and investigate the import company about the briefcase before his big date.
Danno promptly walks in and gives his real name while carrying his badge and gun, and gets made by the bad guys in about 3 minutes (right before he could give them his social security number). Not too bright, especially considering how years earlier, he was twice indicted for murdering kids and his mug was all over the news. And even worse? McGarrett just lost Chin Ho recently to a botched undercover operation because he was too well-known. Poor Chin’s corpse was still warm by the time Danno went undercover.
Why would the producers allow such stupidity? Because the plot required it once again.
Sadly, all they had to do to preserve Danno’s intelligence would be to have him wear Steve’s “Short Walk on the Longshore” hairpiece, a fake moustache, change his name to Stan Gilliams, and leave his gun and badge at home. The bad guys still would’ve discovered he was a cop thanks to all their cool evil gadgets (fingerprint chair, x-ray clock, etc.) and the plot could’ve proceeded as normal while making him appear sane, all while still joking at the end about him not getting laid.
Naturally, since Danno managed to survive this case despite Steve’s best efforts to get him killed, what does Steve do shortly after? He sends Danno undercover with Nazis.