Wearing their birthday suit - Idioms by The Free Dictionary
wearing (one's) birthday suit (redirected from wearing their birthday suit)
wearing (one's) birthday suit
Completely naked. Alludes to the fact that one is born without clothing. I have a recurring nightmare where I'm walking through school wearing my birthday suit. As kids, we had no problem going swimming together wearing our birthday suits.
References in periodicals archive
This is a sign that hates being restricted - you may well find them wearing their birthday suit
(which for those of you who don't know the expression, means stark naked!) you prefer rich purples, dark blues.