Is there a word, phrase, or idiom for a person who stays too late at an event such as a dinner party?

Something like "latecomer" but for departing rather than arriving.

For example, "Bob was always the _____ at social outings."

Other variations with verbs or non - noun idioms are useful to me as well, such as "Bob would always ________ at social outings."

Solution 1:

Guests who stay too long can be said to overstay their welcome or wear out their welcome. That is, their host grows tired of their presence and wishes they would leave.

The idiom is not limited to "staying too late," and also applies to other sorts of unwelcome behavior:

To behave in an offensive, burdensome, or tiresome manner, with the result that one's continued presence is unwanted within a residence, commercial establishment, or social group. (WT)

The overstay variant, though sometimes considered synonymous with the wear out version, more strongly emphasizes the length of the visit. It is more commonly used in British English (ngram), while wear out is more popular in American English (ngram).

The verb overstay by itself also communicates the act of staying too long, but less idiomatically (WT). If you require a noun, some derive overstayer (WT) from the verb, as used in a LifeHacker article:

People won't always get your subtle hints. Sometimes you need to tell an overstayer directly that the conversation and hang out time is over.

Solution 2:

The word "straggler" comes to mind, meaning "a person or an animal that is among the last or the slowest in a group to do something, for example, to finish a race or leave a place."

Example sentences:

‘The majority have returned to breeding grounds by late March, but stragglers have lingered locally until the end of May.’

‘The library was nearly deserted except for a few stragglers checking out books or reading in corners.’

‘No, the last stragglers, the tourists and the visitors, have now left the palace.’