A good way of concealing diapers under your pants is to use and wear a onesie or diaper shirt that snaps in the crotch over the diaper.
I wear a onesie when in public as it helps to conceal the diaper should my shirt ride up when I bend over and also prevents the diaper from sagging when it gets wet.
You could also wear a pair of boxers or underwear over the diaper to conceal the diaper from your friends and other people.
Wearing regular underwear or boxers and/or a onesie over the diaper can help keep the diaper out of view from people.
However if the people are really your true friends then they won't make fun of you for having to wear or wanting to wear diapers.