These nights sucks. Sucks is an slang word which means bad/unpleasant etc. If you are going to "These nights suck" suck will become verb, the phrase now says your nights is sucking...
Ex. Dogs suck their mother's nips. Dog sucks his mother's nip.
If you are going to use.it on singular. "This' sucks" or "This is sucks" remember that sucks is slang adjective.