If I sleep in PJ's I dont wear knickers, but I dont like sleeping in them, its to uncomfy, only do it if Im cold and DH hasnt come to bed yet, normally wake up in the middle of the night and take them off.
I have always told my DD now 16 to let her bits breathe, she wears knickers under PJ shorts if she is lolling round the house but takes knickers off to sleep in.
My mum also said bits should breathe.
PMSL at toot-toot residual :)