As commuters face a week of misery, hapless Mr Corbyn threw his weight behind the hated train unions "because I think Southern Rail have behaved in a bad manner".
Frankie, who lives in Hove, says in the letter that both his parents work in London, and that he is exhausted of them coming home late because of rail strikes.
Some commenters on social media suggested Corbyn would "need protection" if he joined protesting drivers on the picket line.
Today's strike is the first of three this week, with further walkouts set for tomorrow and Friday.
Meanwhile, it is back to business for London Underground.
A Southern Rail train.
Southern, run by Britain's largest train operator Govia Thameslink Railway (GTR) - a joint venture owned by London-listed Go-Ahead GOG.L and France's Keolis, said nearly none of its 2,284 services would run and advised its customers not to travel.
This is the very reason behind the Southern walkouts, which began after a six-month-long dispute between Southern Railway and the RMT union over the roles of Southern's conductors.
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About 200 bus and coaches will ferry passengers from eight Southern stations to those run by other operators. "I pay £5k for no service".
The company also advised people to work from home or remotely if they can, and to stagger journeys if they can't.
The rail franchise warned passengers that there would be limited services or no services at all on some lines due to industrial action and told commuters to travel only if necessary.
"The unions' response is utterly disproportionate, causing misery to 300,000 passengers a day across the South East and untold damage to the regional economy".
Commuters took to Twitter to vent their frustration over the strikes this morning as union members walked out today (Tuesday, January 10).
Calling on train unions to return to the negotiating table to resolve the dispute, Transport Minister Lord Ahmad said: "It's gone on far too long".
"We remain committed to a negotiated settlement, as was reached with ScotRail, but it is hard to negotiate with people who are not prepared to be flexible".