Is the plural of penis, penii or penises, whatever...

We were all at this most funky but fabulous dumpling joint in Chinatown Melbourne off Little Bourke Street, at a restaurant called (what else but 'Shanghai Dumpling'). It was crowded, railway-station grade noisy and reminiscent of Wan Chai in Hong Kong. In this packed space there was this long table with wild women celebrating a girl's night out, a hen party for a soon-to-be bride. Yup, that's right she was wearing this penis hair band (with intermittent flashing lights!) and more. I couldn't resist a shot of this innocent face....