I'll have to check my schedule. - The worst way to say no. It sounds like you care, but you do

The worst way to say no. It sounds like you care, but you don’t. You just want to escape.

'I’ll have to check my schedule.', said when you asked them to the concert.

'Check your schedule.', said when you invited them to the beach.

'Check your schedule.', said when you showed up at their door unannounced.