Lol! Just googled it now:
Loaded for bear: An allusion to equipping oneself with the sort of heavy weaponry suitable for hunting large game.
I missed the part where it meant this:
<www.dictionary.com/browse/loaded--for--bear>
Fully prepared for action; also, spoiling for a fight. For example, Bill tackled his new sales route loaded for bear, or When Martin was three hours late, his wife was loaded for bear.