Green’s Dictionary of Slang

1. of a task, harsh, demanding; also in fig. use.

1919

A. Lunn Loose Ends 27: ‘It’s a sweaty house for new men.’ Cluff shook his head sadly. ‘Yes, it’s a hard life for new men.’.

2. (UK juv.) of a person, very unpleasant or unattractive.

2001

OnLine Dict. of Playground Sl. 🌐 sweat(y) adj. something or someone you found particularly ugly/unsavoury/ horrible; e.g. ‘He is so sweaty!’.