Charity should at all times govern our speech so that we avoid such faults as slander, detraction, quarrels, harsh and unfriendly criticism, rude and short answers, complaints when asked to do a service, excessive teasing and ridicule. (134, my emphasis)
Apparently only excessive teasing is against charity. Fr. John goes on:
Excessive teasing also fails against brotherly love. You might say that some people like to be teased, yes, they even take offense if they are left to themselves and not taken notice of. This may be true, yet there is no one who finds a joke or pleasantry enjoyable if it is mixed with gall. Those who are inclined to pass a joke at the expense of another, or enjoy teasing others, should be very careful not to overstep the bounds of charity and should have the proper sense of judging what will be within the limits of legitimate amusement and what will rather hurt and offend another. (135)
In other words, teasing does have a place in religious community, even as a work of charity. Anyone who has been in religious life knows that sometimes humor is the safest vehicle for fraternal admonition and one of the quickest means of deflating those who struggle with temptations to vanity.