It IS an expression. Christ or God doing something is traditionally changed into something 'safe' from what it really means to prevent blasphomy. For example, 'Cor Blimey' means 'God blind me' as an expression of surprise.
In this instance, and I'm only summising, Christ on a bike means 'Christ blind me', but you'll have to check with God to get the definative answer.
BTW: this all stems from the fact that blasphomy was illegal on-stage during the middle ages so 'zounds' meant 'God's Wounds', and so on. Go check out your Shakespeare for countless examples...