"Hi Spiderman." I reply. Sometimes it's best to treat random with normality.
He continued to stare.
Then it was gravely stated.
"It's just me Mummy in the shirt you gave me."
"Oh, that's good to know." I give a relieved sigh. "I was feeling a bit awkward having spiderman watch me have a shower."
With a giggle and a skip Spiderman disappears and I continue to wash my hair.