Often misused when quibbling about something someone said. In that context, the statement "That's only semantics" would be more aptly phrased as "You're just 'splitting hairs on word meanings."
-- as a blanket repudiation of precise communication.
-- by persons advocating 'subjective feelings' over 'objective description' as a mainstay of communication.
The very concept of semantics is frequently disparaged by wishy-washy passive-aggressives who refuse to be accountable for their careless use of language or their deplorable lack of education.
Skater-boy was too lazy to choose his words carefully, unaware that without semantics, even his street drivel would be incomprehensible.