In the Worms 3D wormopedia they refer about flipside and sewerside religeons.

if you declare these as real worm religeons what do you reckon thier holy weapon would be?

they're sub-sects of the major worms religions. if I remember correctly, they're both simply grey-side variants.

Flipside was a joke side about players who are incredibly lucky regardless of strategy.

Sewerside was a joke side about players who are suicidal and prefer making big explosions to actually winning. I guess their favourite weapon would be Armageddon.

I thought sewersiders would be starburst (worms 4)

Kamikaze immediatly sprung to my mind. But whatever floats sinks your boat.