Next to me at Mass was a most pious young man, who seemed to have brought not one but three or four books of devotion with him. He spent the whole of the time before, during and after Mass going rapidly from book to book (I noticed during the chanting of Terce he was busy at orisons in veneration of the Five Wounds), not merely reading but mouthing the words in what became a rather noticeable whisper. I had to lean over to him after the Sanctus and very quietly, kindly but firmly, say, "Excuse me, but could you read silently? It's very distracting. Thank you." At that time of the Mass, the priest alone recites the Canon at the altar – we don't need a second celebrant of the liturgy in the pews!
Now, I have been guilty of exactly the same unwitting displays of overzealous piety when in the throes of devotion, but I did finally realize what was meant in an old handbook for novice masters, when it stated that one of their duties was to teach their underlings to pray silently. No less a man than St Augustine stood in amaze when he beheld St Ambrose reading silently, since in antiquity one always read aloud; but we have moved on from this. In piety, less can be more: I have been there, done that, what with chugging through an enormous self-imposed round of prayers gathered from divers sources, and, by being melodramatic, appearing most singular and odd; indeed, I probably often still fall in that category – but at least I have some self-awareness about curbing this.
That said, long years ago I was warned in a friendly manner by a priest about indulging in dotty displays of devotion: one shouldn't draw attention to oneself, let alone inflict one's own discipline and penance on others. To that good Catholic I sat next to, I would say now what I would in all kindness have hoped to say then: Your zeal and love of God is commendable, and please do not be offended, but in prudence moderate your outward manifestations of piety, lest some mock and others be exasperated. God bless.