I'll give you the short version, as since I'm an ex-smoker who vapes (uses an e-cigarette), I'm very much involved in trying to get the various senseless rules against them (at the EU, national and TOC level) overturned or stopped in their tracks. You don't want to know the full details - or I might exceed any word limit this forum has for postings!
I constantly use my e-cig on trains, but in "stealth" mode - holding in the vapour so that there's nothing visible. No vapour, no problem! I avoid doing this when train staff are around, since I don't want to get into an argument with them about a policy they had no hand in making, but might be expected to enforce.
The TOCs seem to be all falling into line (if they haven't all already done so) with the British Medical Association's completely groundless, scientifically unfounded opposition to e-cigarettes, and making it company policy to forbid their use; even though they have no obligation to under legislation.
(My deep objections to this kind of "legislation by oligopoly decision" are another story; as is the BMA's Martin McKee's strident and strictly political rather than scientific or medical objection to e-cigs; as is the general level of scare-propaganda surrounding the subject).
I completely understand your reluctance to have vapour blown in your face: even though all research indicates it's absolutely harmless, it can still feel like an impolite intrusion on your space. This is why I "stealth-vape" in enclosed spaces such as trains.
Personally I think a bit of courtesy and mutual agreement between fellow passengers would go a long way on this subject. The heat has been stoked up, though, because almost all vapers are, like myself, ex-smokers, and having been thoroughly wound up by the demonisation of smokers over the past couple of decades, have now succeeded in giving up smoking only to be demonised again by the "public-health" establishment and legislative bodies!