Stand/stick out like a sore thumb
Definition 1 of 1
Pro Tip 1/3Visual Imagery
This phrase creates a visual image to describe something that doesn't fit in. 
Wearing a Halloween costume to a wedding would make you stand out like a sore thumb.
Pro Tip 2/3Metaphorical Use
Metaphorically, it suggests awkwardness or not fitting into a social context. 
Being the only adult at the kids' table made him stick out like a sore thumb.
Pro Tip 3/3Negative Connotation
Often implies an undesirable or unintended level of attention. 
He tried to blend in, but his accent made him stick out like a sore thumb.