I can only imagine you'd be making them as a joke gift, I agree with others they really can't be comfortable because...well...um... never mind.
But if you must, it shouldn't be hard to find a pair of knitted shorts. There are many in woman's sizes. You might have to size up for them to fit a man.
Next, I found several banana cozy patterns. It'd just be a matter of figuring out where to place a hole in the shorts to transition to knitting in the round for the elephant trunk.
Mirl56 at Ravelry, too.
Learn from the mistakes of others. You canít live long enough to make them all yourself. Eleanor Roosevelt
Lady Feb Sweater
more shawlettes, socks